Quote Originally Posted by JimK View Post
Speaking of CH levels, the paperwork that came with my pool states that CH is necessary to keep the liner from becoming brittle. Is this true or BS?
I've several times talked to engineers at the companies that make the vinyl sheeting (not completed liners) and they tell me it is NOT true. In any case, if you did have loss of calcium chloride, it wouldn't make the vinyl brittle. PVC is naturally brittle, with or without calcium carbonate filler -- you have to add a plasticizer to make it flexible. Loss of plasticizer WILL make it brittle.



Quote Originally Posted by JimK View Post
Interesting that this pool calculator, www.poolcalculator.com/ , recommends the same thing. If I type in a CYA level of 80, for SWCGs it recommends a minimum FC level of 4 (ie 5%).
As Waterbear notes, it's not exactly a coincidence.


Quote Originally Posted by waterbear View Post
50 to 80 ppm is recommended for biguanide pools but there is a very small concern of possible toxicity at the higher levels.
As best I can tell, the toxicity issue applies primarily to folks who have (a) male dogs who (b) drink a lot of pool water, and (c) have not been fixed, but are planned (d) for breeding. Significant borate ingestion can impair canine fertility and is possibly mutagenic. One of the other PF Support Team members does not use borates because she breeds German Shepherds and they do drink a lot of pool water.