White Flakes - Not Calcium

chlorinatorpro

In The Industry
Feb 16, 2016
106
CA
Was at a customer's pool. He thought he was not getting chlorine production from the T-15 cell that he had for 2 1/2 months. There was a thick layer of white flakes that didn't look like calcium and his AquaRite readings were within normal ranges. He was "sure" that his pool water had no issues. Returned to the shop and let the cell soak for 30 minutes in a muriatic acid/water bath. Some calcium came off right away as you could see the fizz however a vast majority of the material just sank to the bottom the bucket. Thoughts? Plaster problems? Tested the cell on my tester and it worked fine. Produced plenty of chlorine. Must have been so coated with this material that the chemical reaction from the plates couldn't happen.
 

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ping

TFP Expert
LifeTime Supporter
Jun 24, 2011
3,134
Long Beach, CA
Post the pool water test results which will help us determine what's going on. Calcium buildup on the plates can prevent the cell from operating properly and is usually due to the CSI of the water being in the positive range.
 

chlorinatorpro

In The Industry
Feb 16, 2016
106
CA
16 hours later the white flakes finally dissolved in the muriatic acid bath.

I don't have any water test results. It was just a general question hoping to find possibilities for what I was seeing.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,367
Tucson, AZ
Has that customer been using any sulfate-containing products in their pool or any metal sequestering agents that contain HEDP?

Calcium sulfate scale dissolves slowly in diluted muriatic acid with no visible fizzing. Calcium phosphate scale only really dissolves in concentrated MA and, even then, very slowly. Both of those scales can form IF concentrations of either phosphates or sulfates are very high. Many times the scale from an SWG can be mixed (calcium carbonate plus sulfates and phosphates) but there usually has to be an external source of sulfates (eg, dry acid use) or phosphates (oxidation of HEDP to orthophosphate).
 

JamesW

TFP Expert
Mar 2, 2011
21,091
I would guess calcium sulfate. The scale has a unique look as described in this article.


Go over the chemicals used in the pool and look for any with sulfur or sulfate.

Some pool stores push sulfuric acid instead of muriatic acid.
 
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JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,367
Tucson, AZ
It usually takes both high CH and high sulfate levels for CaSO4 to scale out (it’s a precipitation reaction that is not pH dependent). If this occurs again, or if you want to avoid seeing this in the future, the only way to deal with it is to partially drain the pool water to reduce calcium and sulfate levels.