I have 9-year old plaster/gunnite 15K pool with very heavy iron staining. I put bottle of sequestrant in monthly but doesn't help.
Normal test results are PH=7.4 to 7.6; TA=70; CH=240; CYA=60; FC=9 to 11; CC=0. Water source is well with high iron and 8 pH. I understand the relationship between high chlorine, high pH, and staining. Think that has been part of the problem. Will do a better job of appropriate FC level, CYA/FC balance, and keeping pH closer to 7.2. Just have to remove the stain first.
I am in the middle of putting citric acid to try to free up the stains. I put the acid in a sock and tested a very stained area in deep end of the pool. Didn't get it all but it did work. Then used sodium metabisulfate to reduce chlorine level. It was at zero yesterday when I started this. With pool on recirculate, I put in 2 1/2 pounds of citric acid around edges of pool; concentrating on deep end, where staining is terribly dark. No obvious removal after 6 hours. I put in another 2 1/2 pounds and still no obvious stain removal. I still have the pool on recirculate and haven't put in any sequestrant yet, because others said you want to wait until the stains are gone before doing that.
Pool temp is 65, pH is now so low I can't measure it, FC is zero, and no amount of scrubbing, brushing, or cussing has helped.
Looking for help with next steps. Also wondering if I have to worry about organic issues since FC is zero...even if pool temp is below 70. Was also wondering if cool pool temp negatively affected citric acid working. Many thanks. rick