Had a couple of dime sized stains when I took over the pool. They disappeared when I got the pool balanced, keeping the pH around 7.5/7.6 July through October. I let the pH rise to 7.8/7.9 through the colder months with no stains.
In the last couple of weeks I've dropped the pH back down to 7.5/7.6 as the temp has risen. In the last week about 30 small stains have appeared, mainly on the shallow end steps.
That doesn't make sense! The only factor I can think of is that as about 6 weeks ago I raised CYA to 50 with 4 pucks dissolving over 3 weeks in a Rainbow feeder half open. FC remained consistent at 7, but pH dropped to 7.2 so I added pH up. Added way too much and had to add MA to bring it back down, all within a couple of hours. Stains have only appeared in the last week, and do appear to fade after MA addition.
Why am I getting these stains at the lower pH? Am I heading for an AA treatment or should I drop pH to 7.2 for a few days and see what happens?
Last nights test results:
FC 7.5 (after small Cl addition)