Odd Stains, not Algae

[GJBenn85]

For a few months now I have been fighting a losing battle with stains in the shady side of the pool. The stains simply do not brush off and they appear to actually be in the plaster; no slimy feeling, nothing brushes off, so I concluded it is not algae (have also been keeping the chlorine higher and been using polyquat). Staining is yellowish-brown in color.

The worst area is a bench on the shady end, second worst being the walls surrounding the bench:




In the first photo, the lighter area about half way over at the edge of the bench is what the aggregate finish should look like. The second photo better shows what I am dealing with.

Pool numbers:

pH: 7.4
chlorine: 4
TA: 80
CH: 200
CYA: 40
salt: 2800

Any ideas on what this is and how I can get rid of the staining?

[waste]

GJB85, welcome to the forum, a good choice! It looks as if it's a metal stain (I suspect iron, but may be wrong on which metal). To test for metal stains, rub some ascorbic acid (pure vitamine C) on the area and see if it disappears. If the ascorbic acid test yields no results, you can try placing a chlorine puck (or small pouch of granular chlorine) on it to see if it's organic. The results of these 2 tests will help the folks here better advise on how to proceed. Looking forward to hearing your results! - Waste

[GJBenn85]

Before you responded I rubbed a vitamin C tablet on the stains and they disappeared instantly. My quick reading on this site says a metal out type chemical (Jack's Magic?) combined with absorbic acid and zero chlorine...right track?

[waste]

GJB, you didn't even need my advice, you knew already what to do! I believe that that is the next step, but I'm not a 'stain expert' (mbar and smallpooldad seem to really know this stuff, as do others). I'd look through the 'stains' area and see what can't be culled from an advanced search. I think that sequesterant then ascorbic acid directly applied can be done for small areas without having to treat the entire pool with ascorbic nor changing the cl nor pH, but please check to make sure that's correct. I'm proud that you knew what to do and somewhat abashed that I can't help further. Best of luck with this!

[GJBenn85]

On Sunday last weekend, I added a sequestering agent and started reducing the chlorine in the pool. On Wednesday, I added the absorbic acid and some more sequestering agent, with chlorine at zero, and switched to circulate rather than filter. The stains have disappeared but now the pool water is very cloudy. I have been running the filter nonstop since Wednesday (and have backwashed it plenty) and started producing chlorine again on Friday. There has been no appreciable difference in the cloudiness in about 2 days worth of filtering. I will check the balance today and post the numbers but is there anything that can be done to speed up the process?

[mbar]

You are seeing the ascorbic acid and metals that have gone back into solution, or precipitated into salts or flakes. This is making the pool cloudy - you can start to bring up the chlorine. You can slowly take it up to the high end of your cya table, and then even higher if you do it slowly and watch for the stains to reappear. Just be sure to keep your ph low while adding chlorine. The pool will eventually clear - you can put a skimmer sock on the skimmer to help catch small particles.

Or, you can use a floc, let it circulate, turn the filter off and let the precipitate fall and vacuum to waste. It is up to you - if you want to add less chemical to the water, then just have POP, and your water will clear with chlorine and filtering. Please ask any other questions you may have