Hey, new to pools but learning a lot. Made the mistake of using granular shock and chlorine tabs the last 2 seasons and not my cya is 200ppm or above. I know I have to water change however with my semi in ground pool I was told to never drain it or it would collapse or the liner would shrink.... I can't find a proper way to get this done. At over 200 ppm cya I know o need to do like 80% unfortunately. Water is expensive here and draining a foot at a time is going to be expensive but I would think this is the safest way. Any recommendations?