Ben,

Thanks for those links. This one says under "Calcium Hardness Check", "Calcium levels should be kept at a minimum level of 200 ppm to avoid corrosive conditions. Calcium levels over 500 ppm may cause problems such as cloudy water or scaling on the liner surface." (this link also says CH should be a minimum of 200 ppm). Of course, the "corrosive conditions" they are talking about are the ones people refer to for metal corrosion if there isn't a thin coating of calcium carbonate and that's a debatable and controversial topic (see this link for one such discussion) and they say nothing about low calcium doing anything specifically to the liner itself. Other CGT links refer to low pH being the real culprit along with very high chlorine level such as found by placing a Trichlor puck on vinyl (which is also low pH). They recommend using Cyanuric Acid, which as we know will reduce active chlorine level so reduce the effects of bleaching for the medium blue that is apparently the only one affected by chlorine.

The link from giroup01 (thanks for that) says the CH should be a minimum of 100 ppm. However, the lab studies looking at different water parameters found that low and high pH were the most problematic while high chlorine levels could fade vinyl and also accelerate the effects of low pH. The ideal pH was between 7.0 and 7.5. Below 7.0 there was in increase in wrinkling, loss of tensile strength, elongation and fading. Above 7.6, the vinyl loses weight and expands. As for chlorine, it should be noted that they had a starting CYA level of 100 ppm which is rather high. The FC of 20 ppm in these conditions adversely affected the vinyl (interestingly, this is only an active chlorine level of somewhere between 0.1 and 0.4 with equivalent FC with no CYA of 0.2 to 0.8 so not really that high and we've had people shock with an FC that is up to 40% of the CYA level without bleaching liners, so I don't know why they saw that unless the chlorine test didn't have CYA the way their pH test did). Unfortunately, they did not test for varying CH, but since their tests were at a CH of 100, that at least doesn't seem to be a problem level in the short-run.

Richard