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Brown water, metals and stains

Water that turns tea brown or rust coloured, often within hours of a big chlorine dose, is almost always dissolved metal and not algae. Iron, and sometimes copper, sits invisible in a lot of fill water, especially well water. Strong chlorine pulls it out of solution, and that is what you see. A shock will not clear it, and more chlorine makes it worse. This page is how to tell, and what the plan asks you to do about it.

A few minutes to check, then a few days of filtering

When this applies

The water turned brown, rust or tea coloured, often after a shock or a top-up from a well.

Your fill water comes from a well and your plan adds a lot of chlorine.

There is a stain on the surface and you want to know whether it is metal or organic.

It is not the fix for green water or for yellow patches on shaded walls. That is algae: see Cloudy, green and what to do about it.

  1. 1Tell it apart from algaeMetal tints the whole body of water evenly, like weak tea, and nothing feels slimy on the walls. Algae grows on surfaces, clouds the water, and feels slippery when you brush it. On “How does the water look?”, pick Tea brown for metal, not Mustard or Green.Mustard and Green start a clearing hold, which holds chlorine at a shock level for days. Strong chlorine is exactly what pulls more metal out of solution, so the hold makes brown water browner.
  2. 2Know why well water browns after a shockWell water often carries dissolved iron or copper that you cannot see. A routine amount of chlorine leaves most of it dissolved. A shock, or any large chlorine addition, oxidises it, and it comes out as brown colour in the water and rust streaks on the surface. When the app knows your fill water is from a well, a plan with a large chlorine dose carries a caution saying so.The brown is not the chlorine failing. It is the chlorine working on the metal, and the fix is to hold the metal in solution before the next strong dose, not to add more.
  3. 3Get a metals testTake a water sample to a pool store and ask them to test for iron and copper. Some home kits test them too.A reading confirms the cause before you buy anything, and tells you which metal you are dealing with.
  4. 4Add a metal sequestrant and run the filterAdd a metal sequestrant, following its label, and run the filter around the clock while it works. If your plan also adds a lot of chlorine, put the sequestrant in and run the filter before that dose. The app does not work out how much sequestrant to use: the label is the dose.A sequestrant holds the metal in solution so the chlorine cannot turn it brown or drop it onto the surface. The filter is what eventually carries it out.
  5. 5Test a stain with a vitamin C tabletHold a vitamin C (ascorbic acid) tablet against the stain for about half a minute. If the spot lightens, it is metal. If it does not, metal is less likely, and the stain may be organic, from leaves or algae.Metal and organic stains look alike and are treated differently. This is the simple check that tells you which one you have before anything else goes in.
  6. 6Keep the rest of your planBrown water still needs its chlorine and its balance. Work the other steps your plan lists as normal. If you were already in a clearing hold for algae before the water turned brown, keep it going: the brown is a separate job, and the overnight test is still what proves the algae is gone.Metal does not replace the pool’s other needs, and stopping a hold early because the colour changed lets the algae come back.

When to call a professional

  • A metal stain that does not lift. Removing a set stain is a sized treatment, and a pool professional can do it safely for your surface.
  • Blue-green stains, or a green tint in light-coloured hair, with no well water involved. Copper can come from inside the equipment, such as a corroding heater, and that needs the equipment checked.
  • The water keeps turning brown after the sequestrant has had time to work.

If your fill water comes from a well, tell the app. It cannot see the iron in your water, but it can warn you before a dose that would pull it out.

Where this comes from

  • packages/chemistry-engine/src/followUp/metalWater.ts: the tea-brown note, the sequestrant and filter step, the pool-store metals test and the vitamin C stain test.
  • packages/chemistry-engine/src/recommendations/generateRecommendation.ts: the well-water caution before a large chlorine dose.
  • packages/chemistry-engine/src/clearing/protocol.ts: Tea brown is not an algae condition and never starts a clearing hold.
  • Trouble Free Pool’s metals guidance, which the engine’s metals note already cites.

Keep learning

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