This summer, one of my return fittings in my fiberglass pool started leaking. My pool was losing over 1/2" of water a day. In order to fix it, a pool professional had to drain my pool below the returns and put some silicone caulk around the fitting. He warned me that I might have to do this again in the future if it starts leaking again and told me not to shock my pool for a few days after doing the repair. I'm getting ready to close my pool and I'm worried that it could start leaking again after being exposed to high chlorine levels and cold water temperatures over the winter. Does anyone know if silicone caulk gets degraded when exposed to high chlorine levels or cold water over a long period of time? If high chlorine levels could potentially degrade the silicone caulk around that return fitting, I might want to consider closing at a lower chlorine level and adding an algecide instead of closing at shock level. My pool pro is going to blow out the lines, add antifreeze, and add a winterizing plug to that return fitting, but that won't prevent it from leaking if the silicone caulk started to fail over the winter since the leak was around the outside of the return fitting and not inside of it.