After repeated bouts with yellowish algae, I finally took the boards advice and purchased a Taylor FAS DPD kit. Spent the weekend draining and trying to establish a reasonable CYA level (was well over 100, looks to be around 60 ish now).
Chlorine numbers had been fairly predictable- I measured 20s through the day yesterday, then took it up to 28.5 last night, then it was 26 at 8 this morning. At that point, I was hoping SLAM process was complete, but I added one more 128 oz bottle of 10% bleach. This should have put my 17000g pool at around 31 or 32 ppm at that point. Then I returned home from work work today only to measure FC at 18 a few moments ago (6:30 pm).
Does this sound correct that it would maintain so well overnight only to plummet during the day? I realize since lowering the CYA, I can expect to lose Cl at an increased rate, but 15 ppm in a single day? Pool does take direct sunlight all day long, but not sure how to fight this algae at this rate of chlorine loss.