I've successfully done the CYA test on the AGP at my previous house many times. I have a new house with a salt water pool now and can't seem to get this test to work. When I first tried it 5 months ago I got a 0 CYA reading. I took a sample to the pool store and they told me the CYA was 75. I was happy with that. I assumed the R-0013 CYA reagent I had was old so I bought a new bottle from TFT Test Kits. Today I tried this new bottle and I'm still getting a 0 CYA reading. The black dot is never obscured at all. Is there something different about measuring CYA in a salt water pool I should know? Maybe my CYA really has gone down to 0 since last November? I doubt it since the Sodium Chloride test says I have 3400 ppm which is good and I hardly ever need to add a bag of salt (3 or 4 bags in the past 6 months) and the pool always looks great. I hate going back to the pool store because they always want to sell me a bunch of stuff.