Neighbor has been using test strips and its been testing OK but he has been using a ton of tri chlor tabs. Turns out they were bad. I got a fc level of 19 but cya level of I am guessing 150 plus. My test strips also showed hings exteemely high So I told him he needs to drain and refill. This is 4 years without emptying. He said that he has to brace it though when its empty or the sides may cave in. Can we lower it 1/3 a few times a refill and get the cya down? Pool is 12k gallons. Any help for him would be appreciated.