Checked CYA approx. one month ago. It was as 30ppm as I wanted. Yesterday I checked again and got under 20ppm. I could fill tube to the top and still clearly see the black dot in the bottom. I'm using tfp test kit. I rechecked 4 times and still got the same results. I have added muratic acid last few weeks as PH has been going up. New vinyl liner installed at beginning of season,I do not know if this would affect PH or not. I'm trying to figure out where the CYA has gone???
I have not had to back wash as our normal rains have not happened this summer. I'm in the process of dissolving granular CYA with the sock/skimmer method to get back to 30-40- ppm. Any ideas on the CYA disappearance??