I'm new and should've paid more attention in chemistry class!! We live in North Texas. (close to Okla) and have a 13,000 gal fiberglass pool with sand filter that came with the house. House was built in 1998 and we've been the owners since 2013. We had a high cya number last summer, but were told that it was OK.....The number didn't decrease over the winter (even with our severe cold snap and 4" of ice on top!) Currently have 110 as cya and no chlorine! We've done some amounts of draining to 'waste' a few times and managed to lower cya from130 down to the present 110. We've had about 4-5" of rain recently and were hoping that would help. With warmer weather coming I'm seeing a little green developing! Hubby will get a pump tomorrow and we will drain more of the pool but will have to drain to street as we are on the low side of our neighborhood and have saturated ground already. Sooooo...hopefully, we can lower the cya over the next couple of weeks? My question to you all......What should I be adding to keep some sanitizer or algaecide in the pool until we can do a significant enough drain to lower the cya? Is diclor the only culprit to cya??