The end of the season, I did an ascorbic acid treatment. I had a CYA of about 60 mid-season, I stopped measuring CYA because I stopped adding tricolor pucks and my understanding was that the CYA should remain steady. To do the ascorbic acid treatment, I dropped FC to zero, I added polyquat60 at the manufacturers recommended amount. When I added the AA it worked like magic and the pH dropped to pH 7.0. I added Metal Magic and I slowly brought up the FC (1 gallon of 12% bleach daily) until FC went up to 6 (6 because I was expecting a CYA of about 50-60). The staining returned, and I was disappointed, but knew that could happen that based on everything I've read. But then I took a battery of readings after everything settled down and my CYA went well under 30! Some cloudiness was evident in the CYA test, so there was still some CYA left but way less than 30. My alkalinity dropped to about 30 as well.
I replaced less than 10% of the water all season, so dilution doesn't explain my drop. Does anyone know whether the polyquat/ascorbic acid/Metal Magic treatment depletes CYA as well? Alternatively could the presence of these interfere with the CYA assay?
I'm glad to have my CYA back down so that I don't need to keep the chlorine as high, but I want to know if there is something else going on.