And if calcium hits 500 (vinyl liner w/o heater), what do the risks relate to? Just cloudy water (esp. if in conjunction with high TA as you said) or harm to one's liner? I believe, but I'm not sure, we like to keep our pH in range for the sake of the liner and our eyes. It appears that TA doesn't affect the liner, just potentially effects clarity of water. If that's so, a lot of people get quite worried over, and expend a lot of effort to lower, high TA often for no reason?