I’ve got a 20-year old fiberglass pool with a mesh cover. Water temperature is now 60 degrees so I thought I’d skip the polyquat this year since it doesn’t seem to help and just close at shock level. I’m concerned, however, about the effect the high chlorine level will have on old our mesh cover and the fiberglass. My mesh cover and gelcoat aren’t in the best shape, and I had a crack in the shell a few years ago that was patched, so I’m a bit worried that a chlorine level of 20 ppm for so long could be damaging. If a chlorine level that high could be damaging to the fiberglass or our old mesh cover, could I close with a lower chlorine level than this and just add more chlorine later this fall or winter, if we get some unseasonably warm weather? Since my pool will be covered and the water will be cold, is it really necessary to get the FC all the way up to 20 ppm at closing?