and low calcium causes them to become brittle! Or at least I was just told when I went to pick up some 12% bleach at the pool store. He was told by his "chemist friend" and even drew out the basic formula for vinyl CH=CH2 to show me all the calcium (CH). I tried to explain what a hydrocarbon was but got quite a perplexed look. We ended up agreeing to disagree and I left with no calcium. I told him to look on the bright side, if he's right they will get to replace my liner that much sooner.