Knowledge Base
Pool care, explained like a friend would.
Clear answers to what your water is telling you, what to add, and why. Written for first-time owners.
Start here
6 short guides, in the order you will need them.
Watch how it works
WalkthroughHow a water test worksA five-step, illustrated walkthrough from scooping a sample to getting your plan.Read →WalkthroughHow to add chemicalsThe safe, simple sequence for adding anything to your pool — animated step by step.Read →WalkthroughClosing & opening your poolThe two guided checklists that bookend the season — each step with its why.Read →WalkthroughProtecting your pool from a freezeWhat to do when a freeze is forecast — four steps, ranked by the damage each one prevents.Read →WalkthroughDraining part of your poolWhen a plan says to replace water: a quarter at a time, where the water can go, and when to stop and call a pro.Read →WalkthroughHow long to run the pump after you add somethingWhy the pump goes on before you pour, how long it stays on, and why the retest waits.Read →WalkthroughKids, pets and pool chemicalsStoring chemicals out of reach, keeping acid and chlorine apart, and who stays out of the water until the retest.Read →WalkthroughComing back to a pool after months awayA pool nobody has tested in months: what to check, in what order, before you add anything.Read →WalkthroughStorms, heavy rain and pollenWhat to do before and after a storm, why the chemistry waits for a test, and how to tell pollen from mustard algae.Read →WalkthroughBrown water, metals and stainsWhy well water browns after a shock, how to tell metal from algae, what a sequestrant does, and the vitamin C stain test.Read →
Understand the basics
Cloudy, green and what to do about itWhy pools go cloudy or green, what really clears them, clarifier versus flocculant, and how to read a pool store’s printout.Read →What each measurement meansPlain-language explanations of every reading — what it measures and why it matters.Read →What each chemical doesWhat every product does, how it’s added, and why the method matters.Read →Choosing your chemicalsLiquid or powder, tabs or a salt cell, drops or strips — the real options for each job and the honest trade-offs of each.Read →After you add chemicalsThe safety and comfort steps that follow any addition — and the reasoning behind them.Read →Types of poolsPlaster, fiberglass, vinyl, tile, chlorine, saltwater — how each changes your routine.Read →Pool equipment explainedPumps, filters, chlorinators, heaters, timers — what each part does for you.Read →Where our numbers come fromThe methodology behind every target and dose — the ratios, the caps, the rounding, and why AI reads but chemistry decides.Read →Why is my pool green?What let the algae grow, what to test before you buy anything, and how a held chlorine level clears it.Read →Cloudy pool water: how to tell the causes apartEarly algae, the filter, calcium or the tail of a shock. What each one looks like on your test, before you buy a clarifier.Read →How many gallons is my pool?Work out your volume from a tape measure, and why every dose is only as right as that number.Read →GlossaryFC, CC, TA, CYA, CH and the other terms on your test, in a sentence or two each.Read →
About poolcntrl
Questions about the free calculatorIs it really free, why it asks for stabilizer, how to check the amount, and why it sometimes refuses.Read →“The pool store tests my water for free.”True, and a good deal. Why poolcntrl is for the other six days.Read →How accurate are we?What we have checked about our numbers, what we have not, and how many real pools that rests on.Read →
The opening and closing list
This list is only for two moments: opening your pool in spring and closing it in fall. No product pushes, nothing else.