Most pool jobs can be done with more than one product, and the aisle never explains the difference. Each guide below takes one job, lines up the real options, and compares them on the same things every time: what the product is, what else it leaves in your water, how fast it works, how pleasant it is to handle, what it costs you per job, and who it actually suits.
Chlorine for day-to-day sanitizing
Five ways to keep chlorine in the water, and each one leaves something behind.
The jobHolding a steady, measurable level of free chlorine in the water every day of the season.
Every chlorine product does the same thing to germs and algae. What separates them is the passenger: most of them add something else to your water at the same time, and two of those passengers never leave on their own. That is the whole decision, and it is why an owner who has poured the same product all season can find the pool getting harder to manage while nothing about the pouring changed.
Liquid chlorine (sodium hypochlorite)
StrengthPool-store jugs are 10% or 12.5%. Plain household bleach is around 6%, so the same job takes roughly twice as much.
What it is
Chlorine already dissolved in water, sold in a jug. You pour it in with the pump running and it is mixed through within the hour.
What else it adds
Nothing you ever have to manage. It leaves a trace of salt behind, far too little to notice over a season.
Speed
Immediate. It is the only common chlorine that can answer "my level is low right now", which is why it is the one used for a correction and for clearing a bloom.
Handling
Corrosive to skin, clothes and car upholstery, so it wants gloves and a flat spot in the trunk. It also fades on the shelf, faster when warm, so buy it fresh from somewhere with turnover rather than stockpiling it.
Cost per job
Cheapest per unit of chlorine of anything on this list, and the heaviest to carry. The hidden cost is that it goes off, so a jug bought in spring and opened in August is weaker than the label says.
Who it suits
Anybody willing to test and pour a couple of times a week, and anybody whose stabilizer is already where it should be.
Trichlor tabs (the pucks in a floater or feeder)
StrengthAbout 90% available chlorine, and about 54% stabilizer by weight — roughly six parts stabilizer for every ten parts of chlorine.
What it is
A compressed puck that dissolves slowly in a floater, an inline feeder or an offline feeder, trickling chlorine in continuously without you doing anything.
What else it adds
Stabilizer, every single tab, and it never leaves the water except by replacing water. Trichlor is also an acid, so a floater walks pH and alkalinity down all season — an owner who keeps adding acid-lowering products and cannot work out why the pH keeps sliding is usually watching their floater work.
Speed
Slow and continuous by design, which is the point and also the limit. A puck takes days to dissolve, so it can never answer a low reading today.
Handling
Easy — you are handling a dry puck, not a liquid. The one hard rule is that trichlor must never meet another chlorine product: not in a feeder, not in a bucket, not on a scoop. The combination can catch fire.
Cost per job
Looks like the cheapest way to run a pool and often ends up the most expensive one, because the stabilizer it builds up can only be undone by replacing water — and replacing water means paying to refill and re-balance the whole pool.
Who it suits
Owners who travel or cannot test often, the early part of a season, and any pool whose stabilizer still has plenty of room. It is a genuinely good tool used in moderation and watched.
Dichlor granules
Strength56% available chlorine, and it carries stabilizer too — close to nine parts stabilizer for every ten parts of chlorine.
What it is
A fast-dissolving granular chlorine, sold as granular chlorine or "quick shock". It is the pool store default answer to almost any reading, partly because it is easy to sell and hard to get wrong on the day.
What else it adds
Stabilizer, faster than tabs do per unit of chlorine — a few bags across a summer is enough to stabilize a pool into a corner without anybody mentioning it.
Speed
Fast. It dissolves readily and works the same day.
Handling
Pre-dissolve it in a bucket and pour the liquid in, so granules do not sit on the floor and bleach it. Same never-mix rule as trichlor.
Cost per job
Middling per unit of chlorine, and it carries the same delayed cost as tabs: the stabilizer it leaves behind is paid for later in water.
Who it suits
A brand-new pool that has no stabilizer yet, where the passenger is a feature rather than a cost. After that, cal-hypo or liquid do the same job with nothing left behind.
Cal-hypo granules (calcium hypochlorite)
Strength65% available chlorine is the usual bag, but the shelf runs from the high forties to the low seventies and the grade changes how much you need.
What it is
A granular chlorine with no stabilizer in it at all. The usual choice when you want a strong dose of chlorine that leaves your stabilizer exactly where it was.
What else it adds
Calcium. That is welcome in a soft-water pool and unwelcome in a hard one, and there is no chemical that takes calcium back out.
Speed
Fast once dissolved, and it wants pre-dissolving in a bucket of warm water first so it does not settle and bleach the surface.
Handling
A strong oxidizer and the one product most involved in pool-shed fires, always by being mixed with something else. One product per scoop, per bucket, per feeder, and keep it dry and away from tabs.
Cost per job
Cheap per unit of chlorine, and cheaper to carry than liquid because you are not paying to move water. The cost that catches people is calcium in a pool that already runs hard.
Who it suits
Soft-water pools, vinyl and fiberglass pools where the surface is not feeding the water calcium anyway, and anyone who wants a big dose without touching stabilizer.
Salt chlorine generator
What it is
A cell plumbed into the return line that passes a current through lightly salted water and makes chlorine out of the salt, continuously, while the pump runs. A salt pool is a chlorine pool — it just makes its own instead of buying it.
What else it adds
Nothing new to the water, because the salt is recycled rather than consumed. What it does do is push pH up steadily as it runs, so a salt pool usually needs acid more often than it needs anything else.
Speed
Continuous and adjustable, but slow to respond. Turning the output up will not rescue a pool that has fallen behind, so most salt owners still keep a jug of liquid chlorine for exactly that.
Handling
The easiest of the lot day to day — there is nothing to carry or pour except the occasional bag of salt. The cell needs inspecting and sometimes cleaning, and cold water makes most cells stop producing altogether.
Cost per job
The highest up-front cost here by a wide margin and the lowest running cost. The cell is a wear part with a life measured in seasons, so the real arithmetic is the replacement cell rather than the salt.
Who it suits
Owners who want the pool to look after itself and are happy to test and adjust pH regularly. It removes the chore of chlorine and adds the chore of acid.
If you use household bleach
Ordinary laundry bleach is the same chemical as liquid chlorine, just weaker, and plenty of owners use it. Three things matter. It must be plain and unscented — no scented, no "splashless" or thickened kinds, and nothing with detergent or cleaner added, because those bring surfactants and dyes into your water that chlorine will not remove. It is much weaker than pool-store liquid, so tell the app the strength on the label rather than letting it assume. And bleach has a date on it: it loses strength on the shelf like everything else in this family, so an old bottle does less than it says.
One product per scoop, per bucket, per feeder
This is the one genuinely dangerous mistake in pool care. Different chlorine products react with each other, and cal-hypo mixed with trichlor residue in a feeder or a scoop can catch fire or explode. Never combine two chlorine products, never put a different tab in a feeder that held another kind, never reuse an unrinsed scoop, and store them apart and dry.
Why the app never doses tabs for a correction
A tab is a good way to hold a level and a bad way to fix one, for two reasons the app takes seriously. The first is time: a puck dissolves over days, so a reading that is low today is still low tomorrow while the floater catches up, and in that gap a pool with an algae problem gets a worse one. The second is that every tab carries stabilizer that no chemical takes back out, so a dose sized in tabs quietly spends something you cannot get back. So the engine sizes corrections in liquid chlorine or cal-hypo only, and treats tabs as what they really are — a maintenance rhythm to keep topped up, and a stabilizer bill to keep an eye on.
What the app does with it
Tell the app which chlorine you keep and the strength on the label, and every amount it gives you is sized to that jug or that bag rather than to an assumption. Choose tabs and it switches register entirely: instead of a correction it gives you a floater load, a projection of when the floater runs dry, and a running warning about how fast your stabilizer is climbing — and once stabilizer reaches the top of its range it stops asking you to reload the floater at all and tells you to run it empty. If you have a salt pool, the target the app holds you to is set for a salt pool, because a salt cell changes what a healthy chlorine level looks like.
The short versionEvery chlorine product sanitizes; they differ in what they leave behind. Liquid and a salt cell leave nothing, cal-hypo leaves calcium, and tabs and dichlor leave stabilizer that only water replacement removes.
Four things are sold as shock, and one of them does not sanitize at all.
The jobRaising chlorine well above its normal level for a while, to burn through a contamination load or to clear an algae bloom.
Shock is a verb rather than a product — it means taking the chlorine level high on purpose. Four different things are sold in bags and jugs to do it, three of them are chlorine and one of them is not, and the one that is not is the one most likely to send you back to the store for something you did not need.
Liquid chlorine
StrengthThe same 10% or 12.5% jug you would use day to day.
What it is
The plain answer. Shocking with liquid chlorine is pouring more of exactly what you already pour, which is why nothing about it surprises the water.
What else it adds
Nothing to manage — no stabilizer, no calcium.
Speed
Immediate and even. It mixes through in under an hour, which matters when you are trying to hold a level rather than hit it once.
Handling
Corrosive and heavy, and clearing a pool takes a lot of jugs. Store it out of the sun and buy it fresh.
Cost per job
The cheapest way to reach a high level, particularly on a big pool, as long as you can carry it.
Who it suits
Almost everybody, almost always — and it is the only sensible choice when you have to hold a raised level for several days rather than dose once.
Cal-hypo bagged shock
StrengthBags run from the high forties to the low seventies in available chlorine, and the number on the bag changes how much you need.
What it is
Granular calcium hypochlorite in a single-use bag, sold as pool shock. Strong, cheap, shelf-stable, and it is what most people picture when they hear the word shock.
What else it adds
Calcium, every bag, permanently. On a pool that already runs hard, a season of bagged shock is how water quietly ends up scaling.
Speed
Fast, but only once dissolved. Pre-dissolve it in a bucket of warm water, let the grit settle, and pour the liquid in — granules that sink can bleach a vinyl liner or pit plaster.
Handling
The strictest never-mix rule in pool care. Cal-hypo and trichlor together can catch fire, so it must never share a bucket, a scoop, a feeder or a shelf with tabs. Add at dusk so the sun does not waste it.
Cost per job
Very cheap per unit of chlorine and easy to store — the calcium is the price, and you pay it later.
Who it suits
Soft-water pools and vinyl or fiberglass pools, and anyone who wants shelf-stable shock in a shed rather than jugs that fade.
Dichlor "shock"
Strength56% available chlorine, carrying close to nine parts stabilizer for every ten.
What it is
Granular dichlor sold in a shock bag. It works — it is real chlorine and it dissolves easily — and it is the bag the counter reaches for most often.
What else it adds
Stabilizer, in quantity, and nothing removes stabilizer except replacing water. Shocking with dichlor a handful of times a season is one of the most common ways an owner ends up with a stabilizer problem they were never warned about.
Speed
Fast and forgiving, and easier to dissolve than cal-hypo.
Handling
Pre-dissolve, pour with the pump on, and the same never-mix rule applies.
Cost per job
The most expensive of the three chlorines once you count what the stabilizer costs you in water later.
Who it suits
A brand-new pool with no stabilizer at all, where you would have to add some anyway. Beyond that, cal-hypo and liquid do the same job with nothing attached.
Non-chlorine shock (MPS)
What it is
Potassium monopersulfate. An oxidizer rather than a sanitizer: it burns off the sweat, sunscreen and body oils your chlorine would otherwise have to fight, which frees the chlorine up for the job it is there for.
What else it adds
Nothing lasting to the water — but it does something to your test kit. For a few days after it goes in it reads as combined, used-up chlorine on the common drop kits, so an owner tests, sees chloramines that are not there, and buys a shock they did not need.
Speed
It works quickly and swim time comes back sooner than with a chlorine shock, which is most of why it exists.
Handling
A strong oxidizer in its own right — gloves and eye protection, and never mixed with a chlorine product.
Cost per job
Expensive per bag for something that kills nothing.
Who it suits
An indoor pool or a heavily used hot tub, where the load is bathers rather than sunlight and a chlorine spike is inconvenient. It is a supplement to chlorine, never a replacement.
The one that does not sanitize
Non-chlorine shock kills nothing. It will not touch an algae bloom, it will not make unsafe water safe, and a pool running on it alone is not sanitized. That is not a criticism of the product — it does its own job well — but it is sold beside three products that do sanitize, in a bag that says shock, and the difference is not marked on the shelf.
Clearing a green pool is a level you hold, not a bag you add
When shock is being used to clear a bloom, the product matters less than the fact that you are holding a raised level continuously and topping it back up several times a day, for days. That rules out anything you cannot add repeatedly without consequence: repeated cal-hypo means a lot of calcium, and repeated dichlor means a lot of stabilizer. Liquid chlorine is what a sustained hold is done with, because it is the only one you can pour again and again with nothing accumulating.
Add it at dusk
Sunlight destroys unstabilized chlorine quickly, and a shock dose is unstabilized chlorine by definition. Adding at dusk with the pump running gives it the whole night to work instead of half of it to evaporate, and that is worth more than the difference between any two products on this page.
What the app does with it
The engine prescribes liquid chlorine or cal-hypo and nothing else — the two that do the job without leaving a passenger you cannot remove, chosen between on what your water already has too much of. It will never hand you a dichlor dose. It knows about non-chlorine shock for one reason: if you have logged some recently and your combined chlorine reads high, it tells you that the reading is probably the shock rather than a problem and asks you to wait before trusting it. And when you are clearing a bloom rather than correcting a reading, it stops giving you a dose at all and gives you a level to hold, with the top-ups sized each time you test.
The short versionLiquid for anything you have to hold, cal-hypo if your water is soft and you want it out of a bag, dichlor only on a brand-new pool, and non-chlorine shock only when you understand that it sanitizes nothing.
Two acids and one method, and the method is the only way to move them separately.
The jobLowering pH, lowering alkalinity, or lowering one without dragging the other down with it.
Anything acidic you put in a pool lowers pH and alkalinity together — there is no product that moves only one. That single fact is why lowering alkalinity is a procedure rather than a dose, and why the choice here is really two choices: which acid you would rather handle, and whether you also need the method that separates the two readings.
Muriatic acid, full strength
Strength31.45% hydrochloric acid — the standard jug, and the strength the engine assumes unless you tell it otherwise.
What it is
The workhorse. A strong liquid acid that lowers pH and alkalinity together, mixes instantly, and leaves nothing behind but a trace of chloride.
What else it adds
Nothing that accumulates. This is the reason to prefer it over dry acid if you can handle it comfortably.
Speed
Immediate. It is fully mixed within an hour, so you can retest the same afternoon rather than the next day.
Handling
The least pleasant thing in this guide. It fumes, and the fumes corrode metal across a whole shed over time, so it wants storage outdoors or well ventilated and away from your equipment. Gloves and eye protection are not optional, and the rule is always acid into water, never water into acid.
Cost per job
The cheapest acid per unit of work, comfortably.
Who it suits
An outdoor pool with somewhere sensible to store a jug, and an owner who is comfortable pouring a strong acid carefully.
Muriatic acid, low-fume or diluted
StrengthUsually 14.5% to 20% hydrochloric acid, sold as low-fume, safer, or reduced-fume acid.
What it is
The same chemical in a weaker solution, which is genuinely more pleasant to open and store. It is the same acid doing the same thing, just less of it in the jug.
What else it adds
Nothing that accumulates, exactly like the full-strength jug.
Speed
Immediate, the same as full strength.
Handling
Noticeably easier — far less of the vapour that makes the full-strength jug unwelcome in a garage, though it is still an acid and still wants gloves and eyes covered.
Cost per job
More expensive per unit of work, because you are buying and carrying more water for the same effect.
Who it suits
Anyone storing acid in a garage or near equipment, and anyone who has been putting off pH corrections because they dislike opening the jug.
Dry acid (sodium bisulfate)
StrengthSold at about 93% pure sodium bisulfate; the rest is inert filler, and it comes in one grade rather than several.
What it is
A granular acid. Dissolve it in a bucket and pour it in, and it does the same job as muriatic with none of the fumes and none of the splash risk.
What else it adds
Sulfate, which stays in the water and builds up year after year. Nothing about that harms a swimmer, but at high enough levels it can attack plaster and grout, and the only way it leaves is with the water. This is the honest reason to prefer muriatic where you can handle it.
Speed
Same day, once dissolved. Pre-dissolving is not optional — undissolved granules on a floor make a low-pH spot that etches.
Handling
Much friendlier: a bag rather than a jug, no fumes, no corroded shed, and nothing that can splash a strong acid at your face. It is still corrosive enough to want gloves and to be kept out of your eyes.
Cost per job
More expensive per unit of work than full-strength muriatic, and the cost people miss is the sulfate, paid for years later.
Who it suits
Indoor pools, tight equipment rooms, anybody nervous about liquid acid, and cold climates where a jug in an unheated shed is unwelcome. Also a very reasonable default for a small pool, where the yearly sulfate load is modest.
Acid plus aeration (for alkalinity only)
What it is
A method, not a product. Acid takes pH and alkalinity down together; aeration — running your jets, a fountain, a spa spillover, or anything that agitates the surface — brings pH back up on its own without raising alkalinity at all. Alternate the two and alkalinity walks down while pH returns to where it belongs.
What else it adds
Nothing at all on the aeration half. It is one of the very few things in pool care that moves a reading with no chemical.
Speed
Slow on purpose. It is a cycle repeated over several days rather than one afternoon, and trying to shortcut it by pouring more acid just drives pH somewhere unpleasant.
Handling
The acid half carries whatever handling its jug or bag carries. The aeration half costs nothing but pump hours and a little patience.
Cost per job
The acid you were going to use anyway, plus electricity. There is nothing extra to buy, which is exactly why nobody at a counter will suggest it.
Who it suits
Anyone whose alkalinity is genuinely high, which is most pools filled from a hard municipal supply. It is the only way to bring alkalinity down without leaving pH stranded at the bottom.
Tell the app the strength on the label
Strength divides the amount. A jug of low-fume acid does roughly half the work of a full-strength one, so pouring the amount meant for full strength leaves you short and pouring the full-strength amount from a low-fume assumption overshoots. The app asks for the number on your label for exactly this reason, and a stated strength is used only for the acid it describes.
Why lowering alkalinity is not a dose
Ask for a dose that lowers alkalinity and any honest answer is an amount of acid, which lowers pH just as hard. On a pool whose alkalinity is high and pH is fine, one big acid pour fixes the alkalinity and leaves the pH somewhere the water can etch a surface. That is the whole reason the acid-and-aeration cycle exists, and the reason the app hands you a procedure rather than a number.
Acid into water, never water into acid
If you pre-dissolve anything or dilute anything, the acid goes into the water and never the reverse. Water poured onto concentrated acid can boil and spit it back at you. And whichever acid you use, add it with the pump running and spread out along the edge, because a concentrated slug sitting in one place is how a surface gets etched.
What the app does with it
You tell the app which acid you keep, and it prescribes in the units you own — fluid ounces of muriatic, or ounces by weight if you keep dry acid, converted for you rather than left as a note saying "use a bit less". State the strength of your muriatic jug and the amount is sized to that jug. For pH alone the app gives you a verified amount when your test kit gave it enough to work with, and a clearly labelled estimate when it did not, so you always know which one you are looking at. Acid never gets a rough container phrase like "about half a jug" — the amount is always exact, because over-pouring acid is the one mistake here that cannot be undone by waiting. And when your alkalinity is the problem, it gives you the acid-and-aeration cycle rather than one large pour.
The short versionMuriatic if you can store it, low-fume or dry acid if you would rather not, and remember that lowering alkalinity is a cycle over days rather than a single dose.
Three powders and one free method — and the free one is often the right answer.
The jobRaising pH, raising alkalinity, or raising one while leaving the other roughly where it is.
Going up is easier than going down, because here the products genuinely do separate. One raises alkalinity and barely touches pH, one raises pH and takes alkalinity with it, one raises pH and almost nothing else, and one is not a product at all. Knowing which reading you actually want to move is most of the job.
Baking soda (sodium bicarbonate)
What it is
Exactly the same thing as the box in your kitchen, sold in a sack. It raises alkalinity and nudges pH only slightly, which makes it the precise tool for low alkalinity.
What else it adds
Nothing unwanted. Alkalinity is the thing you are raising, and the small pH rise that comes with it is usually welcome anyway.
Speed
Same day. It dissolves readily and mixes through in an hour or two.
Handling
The gentlest thing in this whole guide. You can broadcast it straight across the surface with the pump running — no bucket, no gloves beyond keeping dust out of your eyes.
Cost per job
Cheap, and cheaper still bought as a bulk grocery sack rather than a pool-branded bag of the identical chemical.
Who it suits
Anybody whose alkalinity is low, which is the usual reason pH will not stay where you put it. Fix alkalinity first and pH very often settles itself.
Soda ash (sodium carbonate)
What it is
A stronger relative of baking soda that pushes pH up hard and raises alkalinity meaningfully at the same time. It is what most "pH increaser" tubs contain.
What else it adds
Alkalinity, whether or not you wanted it — which is the catch. On a pool with low pH and alkalinity already in range, soda ash fixes the first and breaks the second.
Speed
Fast, and that is part of the risk. Added too quickly or dry it can cloud the water for a day while calcium comes out of solution.
Handling
Strongly alkaline. Pre-dissolve in warm water, add slowly with the pump running, and keep the dust out of your eyes.
Cost per job
Inexpensive per tub, and the cost that catches people is a second correction to bring alkalinity back down afterwards.
Who it suits
A pool where pH and alkalinity are both low and you want one product to do both. It is a poor choice when only pH is low.
Borax
What it is
Sodium tetraborate — the laundry booster. It raises pH with very little effect on alkalinity, so it is the tool for the one case soda ash handles badly.
What else it adds
Borates, which stay in the water. In moderation many owners consider that a benefit, because borates dampen pH drift and discourage algae; in quantity it is another thing accumulating in water you did not plan to change.
Speed
Same day, once dissolved.
Handling
Easy to handle and easy to buy, and it should be pre-dissolved before it goes in. Harmful if swallowed, so keep it away from children and pets like anything else in the shed.
Cost per job
Cheap per box, and it takes a surprising amount to move pH in a large pool.
Who it suits
A pool whose pH is low while alkalinity is fine — usually a salt pool or one that has been aerated hard. It is the enthusiast option here, and it is a sound one.
Aeration
What it is
Agitating the surface — jets angled up, a fountain, a spa spillover, a waterfall, even a running return breaking the water — drives dissolved carbon dioxide out of the pool, and pH rises on its own as it goes.
What else it adds
Nothing whatsoever, and it leaves alkalinity completely untouched. It is the only way to raise pH without putting anything in your water.
Speed
Slow. It works over a day rather than an hour, and how fast depends on how vigorously the surface is moving.
Handling
Nothing to handle. There is nothing to buy, carry, store or spill.
Cost per job
Pump hours, and nothing else.
Who it suits
Any pool with pH low and alkalinity in range, which is very common. It is also the standing recommendation for salt pools, which tend to climb back on their own anyway.
Alkalinity first, pH second
Alkalinity is the buffer that holds pH still. When alkalinity is low, pH wanders no matter how often you correct it, and every correction you make is undone within days. So when both readings are low the order is not a preference: raise alkalinity with baking soda, let the water settle, and retest before deciding pH still needs anything. It very often does not.
Why a pH increaser sometimes clouds the water
Pushing pH up quickly can make water drop some of its dissolved calcium, which appears as a fine white haze a day or two later — especially in a hard-water pool. It is harmless and it clears with filtration, and it is largely avoided by pre-dissolving, adding slowly, and going up in stages instead of all at once.
What the app does with it
The app is deliberately conservative about raising pH, and this is one of the few places it will decline to give you a number. When pH is low and alkalinity is fine it tells you to aerate — no chemical, no dose, no purchase — because the relationship between an amount of soda ash and a resulting pH depends on your water in a way the engine cannot honestly model. When alkalinity is low too, it sizes baking soda, which raises both together, and asks you to retest before doing anything more. Borax is a product it knows about and never prescribes, for the same reason. If you would rather use soda ash you can, and the app will read the result at your next test either way.
The short versionBaking soda for alkalinity, aeration for pH on its own, soda ash when both are low and you want one product, and borax when you want pH up and alkalinity left alone.
Three ways to add it, no way to remove it, and two of them are accidents.
The jobGetting enough stabilizer into the water to stop sunlight destroying your chlorine — and no more than that.
Stabilizer is sunscreen for chlorine. Without it, a sunny day burns off most of what you added by the afternoon; with too much, the chlorine you carry is held so tightly that it stops doing much work, and your target climbs to a level that is expensive to hold. What makes this the most consequential choice in pool care is the asymmetry: adding it is easy, and the only way to remove it is to replace some of your water.
Granular stabilizer (cyanuric acid)
What it is
White granules or a fine powder, sold as stabilizer, conditioner, or cyanuric acid. The deliberate way to add it, and the one where you decide the amount.
What else it adds
Nothing but stabilizer, which is exactly the point.
Speed
The slowest thing in this guide, and the source of most overshooting. It dissolves reluctantly and the reading can take up to a week to settle, so an owner who retests after two days, sees no change and adds more has just doubled a dose that cannot be undone.
Handling
Pre-dissolve in a bucket of warm water, or put it in a sock in the skimmer basket. Thrown in dry it sits on the floor for days doing nothing and can stain. It is a mild irritant, so gloves and no breathing the dust.
Cost per job
Moderate per tub, and it is a once-a-season purchase rather than a running cost.
Who it suits
Any pool that needs stabilizer, if you can be patient. Add less than you think you need and wait a week before deciding.
Liquid stabilizer
What it is
The same cyanuric acid already in solution, sold at a premium as a fast-acting or quick-dissolving conditioner.
What else it adds
Nothing extra, though some products are carried in something that will nudge other readings — worth a glance at the label.
Speed
Genuinely faster to read back, which is its whole selling point. You are not waiting a week to find out what you did.
Handling
Easier: pour it in, no bucket, no sock, no dust.
Cost per job
Noticeably more expensive for the same amount of stabilizer. You are paying for the dissolving.
Who it suits
Somebody who wants to correct a low reading and retest without a week of uncertainty in between, and anybody who has previously overshot by getting impatient with the granules.
Stabilized chlorine — the hidden source
StrengthTrichlor is about 54% stabilizer by weight; dichlor about 54% as well against a lower chlorine content, so it adds stabilizer even faster per unit of chlorine.
What it is
Not a stabilizer product at all — it is trichlor tabs and dichlor granules. The word "stabilized" on a chlorine label means the chlorine is chemically attached to cyanuric acid, so every tab and every scoop is a stabilizer dose that nobody announces.
What else it adds
Chlorine, which is what you bought it for. The stabilizer is the part that stays.
Speed
Constant and invisible. A floater running all season raises stabilizer steadily, and it is the single most common way pools end up over the top of the range.
Handling
Whatever the chlorine product itself needs.
Cost per job
Free at the till and expensive at the end of the season, because the way out is replacing water and re-balancing it.
Who it suits
Nobody, as a way of adding stabilizer deliberately — the point is to recognise it. A brand-new pool that needs stabilizer anyway is the one case where the passenger is welcome.
It only goes up
There is no chemical that removes stabilizer. It is not consumed, it does not break down at any useful rate, and it does not evaporate. It leaves in exactly one way: with the water it is dissolved in. That is why the app sizes a partial drain and refill in gallons rather than offering you a product, and why the recommendation to stop using tabs for a while is one of the more valuable things it will ever tell you.
Why your chlorine target moves with it
A stabilized pool needs more chlorine to get the same sanitizing effect, because part of the chlorine is bound up and held in reserve. So the right chlorine level is not a fixed number that everyone shares — it is a number that follows your stabilizer reading. This is the reason a pool that was fine last month can be struggling now with no change to your routine: the stabilizer crept up, and the target crept with it.
Add less than you think, then wait a week
Because the reading takes days to settle and the mistake cannot be undone, the only safe way to add stabilizer is to under-shoot deliberately. Add part of what you think you need, wait a week, retest, and top up if it is still short. Topping up costs a tub; overshooting costs a drain.
What the app does with it
Stabilizer is the reading the app treats most carefully. Your chlorine target is calculated from it every single time rather than looked up in a fixed table, so the number you are held to is the one your own water needs. When a stabilizer dose is warranted the app sizes it and reminds you the reading takes up to a week to settle. When your level is over the top of its range it stops asking you to reload your floater and tells you to run it empty, and if the level is high enough that no chlorine level can catch up, it sizes a partial water replacement in gallons — because there is no product answer, and it says so. One thing it deliberately will not do: prescribe against a stabilizer reading that came from a photo of a test strip, because strips read stabilizer too loosely to spend something you cannot get back.
The short versionAdd stabilizer slowly and deliberately, count what your tabs and dichlor are adding for you, and remember that the only way back down is replacing water.
One product, two bags, and the wrong bag overshoots by about a fifth.
The jobRaising water hardness so soft water stops pulling calcium out of your plaster, grout and tile.
There is essentially one product for this job, and that makes it sound like the easiest page in the guide. It is not, because calcium chloride is sold in two grades that look almost identical on a shelf and are not the same strength — and calcium, like stabilizer, is a one-way reading. Nothing removes it except replacing water.
Calcium chloride dihydrate — flake
Strength77% calcium chloride; the rest is water bound into the crystal.
What it is
The common flake or small-chip product, sold as calcium increaser or hardness increaser. It is the grade almost every pool calculator, this app included, assumes when it works out an amount.
What else it adds
Chloride, in an amount no pool ever notices. Nothing else — it is a clean way to move one reading.
Speed
Same day. It dissolves readily in warm water and brushing helps it disperse.
Handling
It gets hot as it dissolves, which surprises people the first time. That is normal and it is why it goes into a bucket of warm water rather than straight into the pool, where a hot concentrated spot can mark a surface.
Cost per job
Inexpensive, and this is the grade with the wider distribution, so it is usually the one in front of you.
Who it suits
Almost everybody, and it is the grade to buy unless you have a reason not to.
Calcium chloride anhydrous — pellet
Strength94% to 97% calcium chloride, with the water driven out of it.
What it is
The same chemical with the bound water removed, sold as hard round pellets — often as an ice-melt product, which is where the price advantage comes from.
What else it adds
The same nothing as the flake. The difference is entirely in the concentration.
Speed
Same day, though the pellets take longer to dissolve than flake does.
Handling
It gets considerably hotter as it dissolves — enough to be worth respecting. Same bucket of warm water, added gradually rather than all at once.
Cost per job
Often cheaper per bag, which is exactly the trap: cheaper per bag and stronger per pound, so buying it and using a flake amount costs you calcium you cannot remove.
Who it suits
An owner who knows they have the pellet, checks the label, and adjusts down. If you are going to buy this grade, tell yourself now that you will use less of it.
The grade changes the amount by about a fifth
Every published calcium amount you will find, this app included, is written for the flake. Weigh out that amount of the pellet and you raise hardness by roughly a fifth more than you meant to, because you are handling a purer product. On a reading that has no way back down, a fifth in the wrong direction on the wrong side of the target is not trivial. Read the bag before you scoop.
Calcium only goes up
Like stabilizer, calcium is not consumed and does not evaporate — it leaves only with the water. There is no calcium reducer worth the shelf space it occupies. So the rule with hardness is the same: undershoot deliberately, retest, and top up. Coming down means replacing water, and if your fill water is hard, replacing water is exactly what put you here.
If your fill water is already hard
On a hard municipal supply or a well, hardness climbs on its own every time you top up, because the water evaporates and the calcium it carried stays behind. Such a pool almost never needs calcium added and will eventually need water replaced instead. The other half of the answer is pH: hard water is manageable when pH is kept toward the lower end of its range, and turns into scale when it is allowed to sit high. Knowing where your top-up water comes from changes the whole shape of this job, which is why the app asks.
Your surface decides whether you care
Soft water is corrosive to anything made of calcium — plaster, pebble, grout, tile — so a plaster pool with low hardness is actively dissolving itself and wants correcting. A vinyl or fiberglass pool has no calcium for the water to take, so low hardness there is far less urgent, though very soft water is still hard on heaters and some equipment.
What the app does with it
The app sizes calcium against the flake, and says so on the card so an owner holding the pellet knows to check. It asks where your top-up water comes from and roughly how hard it is, so the estimate accounts for the calcium arriving in every refill rather than pretending your pool starts from nothing. It also declines to add calcium when the water is already sitting in scaling territory — a recommendation that says "your water is depositing scale" and hands you a calcium dose in the same breath is two answers to one question, so the engine works the saturation verdict out first and drops the dose. And as with stabilizer, it will not prescribe a hardness dose from a strip photo.
The short versionBuy the flake, check the bag if you did not, undershoot on purpose, and if your fill water is hard the answer is usually pH and patience rather than more calcium.
Your dose is only ever as good as the reading it was sized from.
The jobGetting numbers out of your water that are accurate enough to act on, often enough to be useful.
Everything else in this guide is downstream of this page. An amount calculated from a bad reading is a bad amount, calculated precisely — and the ways test methods go wrong are specific and knowable rather than random. The right kit is the one that reads the things you actually act on, at an accuracy that justifies acting.
FAS-DPD drop kit
What it is
A titration kit: you add a powder that turns the sample pink, then count drops of a reagent until the colour vanishes. The number of drops is your reading. There is no colour to judge — you are counting, and the endpoint is unmistakable.
What else it adds
Nothing to your pool. What it adds is confidence, which is the thing every dose depends on.
Speed
A few minutes per full test, longer than a strip and far shorter than a trip to a store.
Handling
Reagent bottles that want a cool, dark cupboard rather than a hot shed, and a little care with the sample. Nothing hazardous.
Cost per job
The highest up-front cost of any home method and the lowest cost per reading, since refill reagents are cheap and a kit lasts years.
Who it suits
Anyone clearing a bloom, anyone with a stabilized pool, and anyone who wants their chlorine and stabilizer numbers to be worth acting on. It is the enthusiast standard for a reason.
DPD comparator kit
What it is
The familiar two-chamber plastic block. You add a tablet or drops and match the resulting colour against printed standards on the side.
What else it adds
Nothing to your pool.
Speed
Quick, and quicker than a drop-count titration.
Handling
Simple, with the same reagent storage rules. Judge the colour in daylight against something white, not in a dim garage.
Cost per job
Cheap to buy and cheap to run.
Who it suits
A routine check on a pool that is behaving. It is a real improvement on strips for pH and for ordinary chlorine levels.
Test strips
What it is
A plastic strip with reagent pads that you dip and compare against a colour chart. The fastest and most widely sold way to test a pool.
What else it adds
Nothing to your pool.
Speed
Seconds, which is genuinely valuable — the best kit is the one you actually use.
Handling
Keep the bottle sealed and dry, and never touch the pads. Humidity ruins a whole bottle quietly, so a strip left on a wet deck ruins more than itself.
Cost per job
Cheapest to start and the most expensive per reading over a season, because you throw each one away.
Who it suits
A quick daily glance at pH and chlorine, a mid-week sanity check between proper tests, and anybody who would otherwise not test at all.
Digital tester or photometer
What it is
An instrument that reads the colour for you and prints a number, removing the human eye from the judgement entirely. Some use the same reagents as a drop kit; some use their own.
What else it adds
Nothing to your pool.
Speed
Fast, and consistent from one person to the next.
Handling
Needs its optics kept clean and its reagents in date, and some models want occasional calibration. A dirty vial is the usual reason a digital reading disagrees with reality.
Cost per job
The most expensive to buy, with reagents that are usually proprietary and priced accordingly.
Who it suits
Owners who find colour matching genuinely difficult, including anyone with colour vision deficiency, and people who value a repeatable number over a cheap one.
The failure that matters most: DPD bleaching out
At high chlorine levels a DPD test can go pink and then go clear again as the chlorine destroys the dye. The result reads as low or even zero chlorine when the truth is the opposite — and that is the exact moment an owner is most likely to be testing, because they are clearing a bloom or have just shocked. The habits that catch it are diluting the sample with tap water and re-reading, or using an FAS-DPD titration, which cannot bleach out. A reading of nothing right after a shock is a reading to distrust.
What strips are good at, and what they are not
pH: genuinely fine. The colour range is wide and the reading is close enough to act on.
Free chlorine: adequate as a rough guide — is there some, is there none — and not precise enough to size a dose from at the top end.
Alkalinity: usable, though it drifts, and it is worth confirming with drops before a large correction.
Stabilizer: weak. The strip pad for it is coarse and the result can be far enough out to send you into a drain you did not need, or leave you short of chlorine all season.
Water hardness: weak, for the same reason, on a reading that also cannot be undone once you act on it.
Reagents and strips both expire
Every method here depends on chemistry that ages. Drop-kit reagents are typically good for a year or so once opened and less in heat, so a kit that lived through a summer in a hot shed is reading from tired chemistry. Strips are worse: the bottle is only good for months after opening and humidity kills it faster than time does, so keep the desiccant in, cap it immediately, and write the date you opened it on the label. If your readings suddenly disagree with how the water looks and behaves, suspect the reagents before you suspect the pool.
How you take the sample matters as much as the kit
Take water from elbow depth away from the returns and the skimmer, not from the surface and not from a jet, and test it promptly rather than after it has sat warming in a cup. Rinse the vial with pool water before filling it. These cost nothing and they remove more error than upgrading from one kit to the next one up.
What the app does with it
The app knows which kit you use and reorders the entry screen to match it, using your brand’s own wording for each reading, so you are copying numbers down the page in the order they appear in front of you rather than hunting. Whatever kit a reading came from, it lands in the same place in your history, so switching kits does not break your trends. It also records how each individual number arrived — typed in by you, read from a strip photo, or carried forward from a previous test — and it treats them differently: stabilizer, water hardness and combined chlorine read by the scanner from a photo are never used to size a dose at any confidence level, because those are the three readings a strip is least able to give and two of them cannot be undone. Nothing is hidden; the reading is kept and the card tells you why it was not acted on.
The short versionStrips for a fast look at pH and chlorine, drops for anything you are about to spend money on, and never size a stabilizer or hardness correction from a strip.
Same tab, three ways to deliver it, and one of them damages equipment.
The jobHolding tabs somewhere they dissolve at a steady, controllable rate — and not somewhere they do damage.
If you use tabs at all, the hardware holding them decides how fast they dissolve, how even the chlorine level stays, and in one case whether your equipment survives the season. The tab is identical in all three; everything else about the experience is not.
Floating dispenser
What it is
A plastic float with a vented base that carries a few tabs and drifts around the pool. The cheapest and most common way to run tabs.
What else it adds
Whatever the tab adds — stabilizer and acidity — the same as any other delivery method.
Speed
Adjustable by opening or closing the vents, but crude, and it varies with how much the float happens to be moving. Expect the chlorine level to wander more than with a feeder.
Handling
Nothing to plumb and nothing to install. Two real cautions: a float that parks itself on the steps or in a corner leaves concentrated acidic water sitting against a surface and can bleach or stain it, and it should be taken out before anyone swims.
Cost per job
Cheapest to buy by a wide margin, and it is a consumable — the plastic goes brittle after a season or two.
Who it suits
Small pools, above-ground pools, and anybody trying tabs without committing to plumbing.
Inline feeder
What it is
A canister plumbed permanently into the return line after the heater, with a dial that meters how much water passes over the tabs. Tabs go in the canister and the pool never sees them.
What else it adds
The same as any tab, delivered more evenly.
Speed
The steadiest and most controllable of the three. A dial setting gives a genuinely repeatable feed rate, so the chlorine level holds flatter between tests.
Handling
Installed once, refilled occasionally. Two rules matter: it must sit after the heater so acidic water never sits in the heat exchanger, and the lid should be opened slowly with the pump off because chlorine gas collects inside. Never put a different type of tab in a feeder that held another.
Cost per job
Moderate to buy, needs plumbing, and cheap thereafter. The lid seals are the only routine expense.
Who it suits
A permanently plumbed pool where tabs are the deliberate long-term plan, and anyone who wants the level to stop wandering.
Offline feeder
What it is
The same idea mounted beside the equipment pad rather than in the pipe, fed by two small tubes tapped into the return line. It can be retrofitted without cutting into the main plumbing.
What else it adds
The same as any tab.
Speed
Nearly as controllable as an inline feeder, with the same kind of adjustable dial.
Handling
Easier to add to an existing system and easier to service, at the cost of two more small connections that can leak. Same slow-lid and never-mix rules.
Cost per job
Similar to an inline feeder to buy, usually cheaper to fit because nothing has to be cut into.
Who it suits
Retrofits, tight equipment pads, and anyone who wants feeder control without re-plumbing the return.
The skimmer basket
What it is
Not a delivery method — a habit. Dropping tabs into the skimmer is common, convenient and the reason a great many pumps, heaters and metal fittings die early.
What else it adds
The same stabilizer and acidity, but concentrated and routed straight through your equipment rather than into the pool.
Speed
Fast and uneven while the pump runs, and then nothing at all when it stops — which is the dangerous half.
Handling
The problem is the pump being off. Water sitting in a skimmer with tabs in it becomes strongly acidic overnight, and on the next start-up that slug goes straight through the pump, the heater and every metal fitting downstream. On a pool with a timer this happens every single night. If you must do it, tabs come out whenever the pump is off — and it is better not to.
Cost per job
Free, and then very expensive.
Who it suits
Nobody. Use a floater, which costs almost nothing and does not do this.
How the hardware changes the feed rate
The dissolving rate of a tab depends on how much water moves over it and how warm that water is. A floater is at the mercy of both, so its output rises in a heatwave exactly when demand rises, but unpredictably. A feeder puts a dial between you and that, which is why a feeder pool holds a flatter level and a floater pool sees more swing between tests. Water temperature drives all of it — the same tab in the same floater lasts noticeably longer in spring than in August.
One product per feeder, always
A feeder or floater that has held trichlor keeps a residue, and putting a different chlorine product into it can start a fire. This is not a theoretical warning — it is the most common cause of pool chemical fires. One product per feeder for the life of the feeder, and if you switch products, you switch hardware.
What the app does with it
Log the tabs you put in — how many and what size — and the app learns your pool’s real burn rate from your own history rather than a textbook one, gets more confident about it the more you log, and tells you when the floater is due to run dry so you are reloading on a schedule instead of a guess. It also tracks what those tabs are doing to your stabilizer and warns you as the level climbs, and once stabilizer reaches the top of its range it stops prompting a reload entirely and asks you to let the floater run empty. One honest gap: the app does not currently ask which hardware you use, so the burn rate it learns is your floater’s or your feeder’s behaviour observed rather than modelled. Logging consistently is what makes it accurate.
The short versionA floater is fine and cheap, a feeder is steadier and worth it if tabs are your plan, and the skimmer is a habit that quietly bills you for a pump.
None of these guides states an amount, on purpose — the amount depends on your pool, and the chemistry engine owns every one the product gives. When you want the actual number for your own water, put your readings through the free calculator.
