My pool is crystal clear. I was told the low Cal can make my vinyl liner brittle and also cause deterioration of pool metals. I have no idea if that is true or not, but I have read that as well. My main concern for the "outside" testing was the salt level-my AutoPilot and my tests were off quite a bit. Now I get this thrown at me and the lower calcium makes me wonder if that could be a cause for the rusting.