Quote Originally Posted by catnip
After the most recent shock with 4 lbs. of Cal-Hypo, the pool went from very clear to moderately cloudy blue for around 12 hours and then fairly clear after 24 hours and eventually very clear. However, there was a residue of what looked white powder scattered around the bottom. The Polaris sweep moved it around but it settled fairly quickly, kind of like very fine snow flakes. Does this sound like calcium carbonate percipitate? Or could it be dead algae (though the quantity of white power seemed much greater than the relatively small amount of visible algae we brushed off)? I vacuumed the white residue to waste and otherwise the pool looks great now.
With your numbers, you aren't severely over-saturated with calcium carbonate in your pool even at a pH of 7.8 while at a pH of 7.5 you are perfectly fine. So I do not believe the precipitate is calcium carbonate. Yes, dumping Cal-Hypo can produce some solids just as dumping some Sodium Carbonate (Soda Ash) can do the same (I've seen the latter myself), but this is pretty obvious clumps and even these tend to dissolve over time.

You can fairly easily determine if the stuff is calcium carbonate by taking some of it (scooped up) and putting it into clean water (tap water is OK, so long as it isn't really high in CH and TA). If the stuff dissolves (give it some time), then it is probably calcium carbonate; if it doesn't, then it could be algae.

Richard