I have read that Dichor ( dichloro-s-triazinetrione dihydrate) is about 57% cyanuric acid. I have only 3700 gallons of water and started using dichlor yesterday. Last night , using the calculator, I took my pool to 3ppm FC. The PH was 7.5. Water is beautiful. I used 2.5 oz by volume to get it to the 3ppm. My CYA was 0. I tested this morning and the FC was 2ppm, PH 7.6. This evening I tested again. FC .5 PH 7.5. I added 3 oz Dichlor by volume to take it to 4 ppm. I waited a few hours and decided to test CYA for the first time. I also tested FC 5 ppm PH 7.6 CYA 0!! I don't understand why I have not built up any CYA. I am using an HTH 6 way tester. The water I put into the clear tube with the black dot on the bottom was crystal clear. I know my test kit is junk. I know I need the whiz bang TF tester but it cant be 100% wrong. How much Dichlor would I have to feed a 3700 gallon pool to get a CYA of 40?