Unknown Staining Issue

mkubiniec

Active member
Oct 27, 2014
28
Mooresville, NC
My pool is slowly developing some staining and I am baffled what it is and how to address it. See the attached photo with the developing brown staining along the edges of the sun deck and steps. I have applied calcium tablets directly to the area - no effect - so not iron. I have applied liquid bleach and muriatic acid directly to the area using a squeeze bottle and tried scrubbing with a scrub brush - no effect. The brownish staining is slowly starting in a few other areas in the pool. I have done the same calcium tablet, bleach and muriatic treatments (with scrub brush) to other areas of the pool (while using scuba) - to no effect.

Full disclosure: last September I confirmed iron staining using calcium tablets and successfully completed the ascorbic acid treatment as posted in TFP. It worked wonderfully. All staining was completely gone. But with the opening of the pool this spring, it seems that this issue has slowly started since about the May timeframe. Also, in early spring, I soaked my filter cartridges in TSP, then thoroughly rinsed off, then in muriatic acid, then thoroughly rinsed off. I did this following guidance from other TSP members to throughly clean the filters to lower the pressure loss across the filters. This procedure worked wonderfully.

A couple of other facts that may be helpful to know: pH is generally in the range 7.5-8.2. It creeps up over time thus requiring the addition of muriatic acid. I have to acid 4-8 cups per week to keep pH in the 7.5-7.7 range. This does seem odd to me considering the pool was built 6 years ago. My SWG produces Cl just fine and I tend to keep it in the range 3.0-7.0. The weather has been quite warm this summer so water temperature is consistently about 88; lately it has been 90-92. All other chemistry parameters are maintained in spec just fine.

I'd appreciate your thoughts on what might be going on and how to address this new staining.

Thanks,

Mike
 

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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
19,405
Northern NJ
Mike, it sure sounds like the stains are from iron.

You mention “calcium tablets” a few times. With iron you use Vitamin C tablets in a paste to see if the stain is iron and lifts.

I would try and give those stains a good dose of Vitamin C.


 
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mkubiniec

Active member
Oct 27, 2014
28
Mooresville, NC
Hello Allen,

Thanks for your reply. My mistake: when I said calcium tablets, I meant to say vitamin C tablets! Per your suggestion, I applied another "good dose" of vitamin C tablets on the staining and lo and behold, the stains would disappear, confirming iron.

Any idea why the iron stains are coming back? Last September I completed the entire treatment protocol using ascorbic acid to remove iron stains. I followed the procedure religiously keeping pH and Cl low for 2 weeks. I also added CuLator packs in the pump filter basket to remove the iron. Do you think I should have done this longer? Added more sequestering agent? Added more CuLator packs? How else is the iron going to be removed from the water if not using the CuLator packs?

I guess I need to repeat this procedure at the end of the swimming season. :(
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
19,405
Northern NJ
If you don’t renew sequestrant periodically it breaks down and releases the iron back into the water.

Iron in pool water needs to be removed by draining or filtering. Filtering takes special techniques with polyfill or filters they can filter down to 10 microns. A cartridge filter cannot do it, a DE filter can.

Culator effectiveness is questionable.