I am concerned about a mismatch in my chlorine test results.
I use a salt chlorinator system and CYA is about 25 ppm (need to increase). I usually test for chlorine with Taylor's FAS/DPD test, and chlorine levels over the last couple of weeks have been (unusually) steady at 4.5 to 5 ppm, regardless of when I test the pool.
Tonight I noticed a lot of larvae swimming up to the lights in the pool, became concerned as to how they could be surviving, and therefore tested my chlorine yet again. Sure enough, about 4.5 ppm (9/10 drops to clear the pink in 10 ml). Suspicious, I tested again using Taylor's R-0001 and R-0002 (bottles new from the store last week). The color suggests about 0.5 ppm and is nowhere near dark enough for 5 ppm. I have redone both tests with new chemicals with the same results. Anyone have any idea what is happening?
I had a black algae outbreak last year and I am now really anxious that the FAS/DPD test has been giving me false readings. Is that possible? I am using Taylor's Speedstir so chems are well mixed...
If consensus is that FAS/DPD is reliable, then can anyone advise re how to kill the gazillion larvae zapping around the pool? Pump is running about 18 hours a day but I guess they swim well enough not to get drawn into the circulation and filtered out, and clearly the chlorine is not killing them.