I closed my pool and as usual, I noticed tiny air bubbles after plugging my returns (maybe one tiny bubble every few seconds). This happens every year and I've never had a problem, but maybe I was just getting lucky. I think it might be hairline faceplate cracks so I plan to replace those next season. So, I always use anti-freeze as insurance. The problem is I have no idea how much to use. I have 3 returns using 1 1/2" PVC. The closest return is about 15-20 feet away. The furthest is about 40-50 feet away. No idea how the lines run underground, but the pressure side leaves for the underground with a singe larger PVC after the SWG cell. So, I assume it splits up into 3 separate lines via an underground tee shortly after. If I total up the amount of 10 foot sections of return lines, it could be well over 100 feet. Given the suggested rate of anti-freeze at 1 gallon per 10 feet of 1.5" line, that could be 12-15 gallons of antifreeze. But then I read that amount is only required if lines are not blown out. So, I have no idea what to use since my lines are presumably near empty at the moment.
Does anyone have any insight as to how much anti-freeze should be used as "insurance" ?