I'm not convinced my CYA reading of 40-50 was accurate. When the new water was delivered, there was no stabilizer in it at all. I added 4 lbs of granular stabilizer, and according to the math on the product, adding 4 lbs to 16,000 gallons of water would raise the CYA to 30 ppm. So I'm thinking I misread the test when I did it. How could it be any higher than 30 ppm if that's how the math worked out in "new" (untreated) water?How did your CYA go from 40-50 yesterday to 30 today? I wouldn't use any more Trichlor tabs or anything else with stabilizer in it until you're confident in your CYA readings.