I have a problem with brown stains at three of the pools I maintain, and I could REALLY use some help/advice on this as the pool store here has got no answers for me. This problem stems back to long before I started taking care of them.
- For my own reference, I will refer to these pools as #1, #7, and #9 in case they go to individual questions.
- All three are indoor pools, all three are painted concrete (with tile borders at the top).
- All three are on SWG systems. #1 is a Zodiac Clearwater LM2-30, #7 was a Zodiac Clearwater until this spring (changed to an Aqua Rite w/ T-15), and #9 is a PoolPilot Digital.
- Two of the pools are maintained with Solar Salt water softening salt, fairly pure stuff. The other is maintained with a Sifto coarse nugget water softening salt.
At pool #1 (which has rounded corners), the staining was the most severe, covering more or less the entire pool bottom, pool walls right up to the tile, and the steps - but lightened to almost nothing at the center of the top. I initially tried to clean these stains with an ascorbic acid treatment (more specifically, Natural Chemistry StainFree + MetalFree just in case it was metals); the result was very odd. I had used this treatment at pool #7 with some success (see below), but at this location the acid merely streaked and mottled the stains, removing only portions of it, even after using nearly 2.5x the normal dose of StainFree. Looked VERY funky.
I ended up having to drain this pool some weeks later for other reasons, and at that time I discovered the color of the stains was about the same color as a coffee stain (the paint is white). Up until then I thought they were green - the water makes it look different While it was drained, I took the opportunity and cleaned the stains quickly and efficiently by pouring straight muriatic acid around the pool walls and mopping it around the pool bottom where it missed. Used about 16L in all (being as merely pouring it down a wall and onto a sloped pool bottom is quite wasteful). The acid would instantly turn yellow upon touching the stain, and within 30 seconds the wall would be perfectly clean and BRIGHT white.
So this pool is no longer a problem, but I am on the lookout for the stains to re-appear. I thought the acid info might be useful to someone. On a side note, AQUA ACID MAGIC is a wonderful product which lives up to its claims. It is a "buffered" muriatic acid; the result of this buffering chemical is an acid that works just as well as standard muriatic, but with almost NO fumes, and it does NOT BURN SKIN. As I said, I used about 16L of the stuff, while standing IN the empty pool, working with bare arms. Not a mark on me from the minor splashes, and the resulting fumes from 16L poured at chest level was about the same as the fumes from 100mL of standard muriatic acid.
Anyway, back to it. At pool #7 (which has square corners), the stains are on the bottom only, right up to the wall. The interesting part is that the stains are more or less only around the outer 10-12" of the pool, except at a corner at the deep end which never has sunlight hit it through the windows, the stain covers the entire corner (about 8' x 10', in an 18' x 36' pool). I did a StainFree treatment here once, using a double dose, which took away about 75% of the stains and lightened the rest; however they have slowly come back and darkened over the last few months, so I don't know what to do.
At pool #9, the same stains exist in a similar fasion to #7 - around the edges, more where there is never sunlight - but not as severe as the other two pools. Getting worse by the month, though.
Does anyone have any ideas what can be causing these stains?