How to remove iron and well water stains from a pool

With ascorbic acid and a metal sequestrant, with the pool still full. Confirm it is iron first by holding a vitamin C tablet on the stain. Then bring the chlorine and pH down to what the treatment's label asks for, add the ascorbic acid and brush, and add a sequestrant so the iron stays dissolved instead of settling back onto the plaster. The full steps are below. Iron stains that are years deep need an acid wash.

Iron, almost always. Well water out here carries dissolved iron, and when it meets chlorine in the pool it oxidizes and settles onto the plaster as tan, brown or rust colored staining.

• Brown, tan or rust colored: iron
• Blue green or teal: copper, often from an old heater core or a copper based algaecide rather than the well
• Dark brown to nearly black: manganese, less common but it does turn up in well water

The stain usually shows first where water is added and where it sits still: around the returns, on the steps and in the deep end. It is most common out in Loxahatchee and The Acreage, where most homes fill from a well.

Hold a vitamin C tablet against the mark for a minute. Ascorbic acid pulls iron straight out of the surface, so if a pale spot appears you have your answer.

Algae also gives itself away: it brushes and lightens. A metal stain does not move at all no matter how hard you scrub.

Light iron staining often comes off with ascorbic acid and a sequestrant while the pool stays full. The step by step is below.

The trap is that this releases the metal back into the water rather than removing it. Without a sequestrant holding it in solution, it settles straight back onto the plaster within a week. Sequestrant is not optional here, it is the entire point.

Because every top up from the well brings more metal in. You can clean the plaster perfectly and stain it again within a season just by filling the pool.

The practical fix is a sequestrant added every time the pool is topped up from the well. The real fix is a whole house iron filter on the well itself, which also helps your fixtures and laundry. Shocking a well fed pool hard can also drop metal out all at once, which is why stained pools often look worse right after a shock.

When the staining is years deep or has soaked into old porous plaster. Chemistry will not lift it at that point, and an acid wash will.

If you are going to that trouble, treat the refill water at the same time. Filling a freshly washed pool with untreated well water starts the whole process again immediately. Acid wash or resurface covers how to tell whether the plaster underneath is still worth washing.

Yes, and for your house as well. Private wells are the owner's responsibility to test, and both the US EPA and the Florida Department of Health recommend testing on a regular schedule.

For the pool, the number you want is iron. Knowing roughly how much is coming in tells you whether a sequestrant on every fill is enough, or whether the well needs a filter before the pool will ever stay clean.