I have been using trichlor pucks over the summer (a lot of travel) and managed to get my CYA levels over 100. The other day we had several days of rain resulting in a little bit of green film around the tile which looked like algae (I am sure it was). FC tested around 6.6 however knowing that my CYA levels were so high, I suspected the algae was a result of lower than effective levels of FC given my CYA level and the rain. I brushed down the pool, ran filter overnight with the inline chlorinator opened wide and the slight green film resolved. I decided to stop using trichlor and used bleach.
According to pool math calculator, to get FC to 11 (given the CYA level), I needed to add about 128 oz 8.25% bleach to my 19k gallon pool. I added 121 oz. Now my FC level is well over 50 the next day. 48 hours later it remains more than 50.
I did have my CYA levels checked twice prior to adding the bleach.
I would Appreciate any input on how I could overshoot from FC goal of 11 to more than 50 with 1 gallon of bleach. I did confirm that it was 8.25% bleach and I did test FC more than once (before and after treatment)
Yes, I do plan to drain half the pool this weekend to correct CYA levels.