Getting pool ready for swimming! Couple of questions...

[chem geek]

If your calcium dropped as well as your CYA, then you likely had dilution of your pool water (maybe from winter rains?). Anyway, with regards to calcium, your vinyl pool (I assume, because it's above ground) does not need calcium carbonate saturation because there is no exposed plaster/gunite/grout to the water.

I am surprised, however, that you report ZERO calcium since even fill water has calcium in it (though rain water probably doesn't). I've never received a definitive answer regarding the use of calcium to help slow down corrosion of metal in equipment, but it seems like a little doesn't hurt so having 100 ppm of calcium hardness (CH) is probably a good idea. I just wish I could be more certain that having no calcium isn't a problem, but I'm not, so playing it safe with some calcium is probably you're best bet.

If you had any plaster/gunite/grout exposed to the water, then I would be recommending the normal recommendation of around 300 ppm CH.

As for stabilizing pH, the easiest way to do that is to lower your TA level to 80 ppm or even 70 ppm (if your CYA is at 30 ppm). Follow Ben's Lowering Your Alkalinity procedure to lower your TA. Also, if you have lots of aeration in your pool (waterfall, fountain) that will tend to make the pH rise faster. If you use a pool cover, your rise in pH will virtually be eliminated, but I think lowering your TA is your best bet -- what was your TA when you experienced this rising pH problem?

Richard