Closing an IG Pool in California??

[chem geek]

I live in Northern California (San Rafael) with similar weather to what you describe. I have solar panels that get drained (by our solar panel vendor) because even a short frost or freeze can ruin such panels (since they are so efficient at transferring energy and have high surface area to volume), but I keep the pump and filter on though at a reduced time schedule of 2 hours/day instead of 8 hours/day (I only switch to this schedule after the pool cools off considerably). I also cut the pool sweep back from 3 hours/day 4 days/week down to 1 hour/day 2 days/week though if your cover goes to the edge and nothing gets into your pool then the pool sweep may not need to be run at all.

I generally add a shock dose of chlorine, keep it uncovered until the chlorine settles down to the still high level of about 10 ppm and I also add some "startup amount" of polyquat algicide for good measure. If you want your chlorine to last longer and don't care about spending a little money, you can also add some non-chlorine shock (Potassium Monopersulfate - KPMS) as well, though most would say that's overkill (and if you already have 50 ppm of Borates in your pool, then the algicide and possibly the KPMS are probably not that helpful). My pool cover is electric so I can open it up during the winter to check on the chlorine and add more if needed, but the chlorine loss is very, very slow. During the summer, my loss is about 0.5 ppm per day (16,000 gallon pool kept at 3 ppm FC minimum) because I keep it covered except when in use (or after the rare shocking) and in the winter it probably loses around 0.5 ppm per week.

The pool generally cools to around 55F in the winter, though gets as low as just below 50F during the coldest part of winter. Of course, nighttime temps can get colder than that -- typically in the 40's -- but the ground temps don't seem to get that cold.

Just out of curiosity, could you measure your CYA when you close your pool and then measure again when you open it and post your results (if you remember!)? I'm going to do that and also monitor my CYA during the summer to try and figure out why and how much CYA degrades over time.

Richard