ph keeps falling

[chem geek]

It sounds like the cover lets UV through -- at least some. That would explain the variation on sunny vs. cloudy days. See if you can check the loss overnight. So add chlorine at night with the pump running, wait at least 30 minutes or up to an hour, then check FC levels (you can then turn off the pump if you don't normally run it at night). In the morning, turn on the pump if it hasn't already started, wait at least 15 minutes, then check the FC level (early in the morning before the sun gets too high in the sky. What is the FC drop? That will tell you if you've got something consuming chlorine other than sunlight.

The loss is normal if the cover lets UV through so let's assume that's the case. The overnight (non-sun) loss is really the key so let's see what that is before jumping to conclusions.

The pH drop is still a mystery. Though you have little splash-out, check the pH of the fill water just in case (maybe there's a leak in the pool -- doubtful though).

Richard

[ljh]

Alk is now up to 100, will try testing for CL at night and again in morning and post results, thanks for the suggestion

[ljh]

last night at 10:30 pm CL was 4, this morning at 6:30 am it was 3.5 with .5 CC. So, should I shock, add algaeside, filter more? I've added 8 lbs of baking soda to move the TA from 80 to 100 and I've added 4 lbs of borax to move the ph from 7.2 to slightly under 7.5 (the color isn't quite 7.5 but definately not 7.2)

[chem geek]

I would shock the pool. At the CYA level of 30 ppm you reported, I would shock to at least 12 ppm FC (Ben's chart says 15 ppm so you can do that instead -- 30 ppm CYA is at the low end of the range) and hold it there until the following three things occur: 1) water is crystal clear (it may already be), 2) FC does not drop overnight or does so minimally (0.5 ppm is on the edge), 3) you do not measure any significant CCs (< 0.5 ppm). So your measurement overnight is on the edge so shocking would be reasonable to do.

[ljh]

okay, will do, I have company coming for the 4th so probably a good idea anyway. The water is crystal clear, but I want to make sure it stays that way. The temp will be cool this week (low 70's day/ 50's night) the water temp has dropped to 76. even with the cover on all day and night.