Chlorine to Stain Correlation?

Michael AP

Member
Jun 11, 2021
5
77018
I’ve been battling bad stains lately and while working through identifying them (with Jacks ID kit) I was told that some liquid chlorines (note: vinyl liner!) actually bring out metals and may result in stains. (I've been through a month of Metal Free, CuLator, Stabilizer, etc. etc. to get to reasonable chemistry ... though a bit hazy still)

My stains seemed to fade after a few containers of ascorbic acid ... and when I went back to tabs while I managed the rest of the chemistry .. but I know I’ll need to get off tabs sooner or later.

I re-added Blue Water liquid chlorine and the stains began to come back the same day!! I’m ID’ing the stain to see if this was a big coincidence, but any truth to the liquid chlorine ‘type’ issue, i.e. do I need to change liquids??

THANKS
 

IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,612
Milwaukee, WI
Pool Size
20000
Surface
Vinyl
Chlorine
Liquid Chlorine
The type of chlorine won’t matter. Just the fact that it is liquid chlorine can be enough. Liquid chlorine is pH neutral in final effect once it sanitizes, but it pushes pH up temporarily when it’s first added. High pH can cause metals to fall out of solution, which leads to stains.

If you can lift the stains and then exchange the water for water without metals, it is the best thing to do.
 
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Michael AP

Member
Jun 11, 2021
5
77018
The type of chlorine won’t matter. Just the fact that it is liquid chlorine can be enough. Liquid chlorine is pH neutral in final effect once it sanitizes, but it pushes pH up temporarily when it’s first added. High pH can cause metals to fall out of solution, which leads to stains.

If you can lift the stains and then exchange the water for water without metals, it is the best thing to do.
Thank you. At first thought, I wouldn't mind keeping the pH up a little to protect against cratering another heater (due to low pH). That said, my readings haven't been near 8.0. What were you thinking for a "High pH" range?
 

IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,612
Milwaukee, WI
Pool Size
20000
Surface
Vinyl
Chlorine
Liquid Chlorine
Liquid chlorine is around pH 13. It mixes into the pool water and thus only increases it a small amount, and then once it oxidizes it lowers the pH back down and so in effect is pH neutral, but you will have localized smaller areas with high pH while it mixes in and that can push the metals out of solution and cause staining. I believe that chlorine also oxidizes sequestrants. That's why adding chlorine can cause metals to fall out and stain.

As I mentioned, the best thing to do would be to lift the stains into the water and exchange it to get the metals all out and fresh water in.
 

Michael AP

Member
Jun 11, 2021
5
77018
Liquid chlorine is around pH 13. It mixes into the pool water and thus only increases it a small amount, and then once it oxidizes it lowers the pH back down and so in effect is pH neutral, but you will have localized smaller areas with high pH while it mixes in and that can push the metals out of solution and cause staining. I believe that chlorine also oxidizes sequestrants. That's why adding chlorine can cause metals to fall out and stain.

As I mentioned, the best thing to do would be to lift the stains into the water and exchange it to get the metals all out and fresh water in.
Ha .... can't argue with that. I accidentally left the hose on for 24 hours and flushed the metals (1.2 Copper) and CYA (117) WAY down.
 
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