Whats the best way to test CYA. I have theTF100 test kit. Hold the test tube at waist level until you see the dot disappear. (Completely). Looks like the test could vary at least 10. Is there a better way to test CYA? What would be a good level to have cya? Right now I'm thinking mine is 50 - 60. Why can you swim when Cya 50 and FC is 5 but when cya is 0 and FC is 4 thats to much?