We have an inground pool, vinyl liner, approx. 22,500 gallons. Last year we battled both high combined chlorine (which was resolved) and high CYA of 173. We stopped using trichlor tablets and switched to liquid chlorine in August. The last test from the pool store (yes, I know... don't trust it and have ordered a Taylor K-2006 test kit) showed the following readings the day before we closed the pool in late August:
FC = 4.6ppm
Alkalinity (w/stabilizer correction) = 139 ppm
pH = 7.7
Cyanuric Acid = 173 ppm
No copper, iron
We were told to drain half the pool and refill to bring down the CYA to an acceptable level. As we thought we would be replacing the liner and would refill with fresh water this spring, we closed the pool. We have not replaced the liner, and have drained and replaced about 500 gallons of water before opening the pool on Monday. Before adding chemicals, the water was tested at the same pool store with the following results:
FC = 0.3
TC = 0.3
pH = 8.5
Alkalinity = 337
Cyanuric Acid = 2 ppm (!)
Obviously, the CYA drop of 171 ppm over the winter seems impossible. Has anyone heard of this before? Could the high alkalinity be masking the CYA? The water temperature is approximately 65 degrees: could this be giving a low CYA reading? After dealing with very high CYA last year, we are very hesitant to adding any stabilizer until we are comfortable that the test results are accurate and won't shoot up later on.. By the way, we are using test strips at home that give a 'low' reading for CYA (<30ppm). We also know that we need to get the FC up, but can't seem to without knowing whether or not to add stabilizer.
Regarding the high Alkalinity/pH reading:
We're not sure the reason for this jump in pH and alkalinity over the winter. In addition to regular closing chemicals, we did have a 'Smart Pool Winter Pill' (enzymes) in the pool over the winter. Could this have caused the higher readings?
We have added 3 gallons of muriatic acid to the pool since opening and using the test strips we now have a pH reading of 7.2, but the alkalinity is still in the 'very high' range. How to get this lower without dropping the pH too much?
The water in the pool is crystal clear for the time being.
Thanks for any advice you can give. I've read through some of this great website for answers, but have not found them yet.