Get a small amount of pH Minus (aka dry acid, etc.). Put about 1/4 cup in a baggie. Swim the baggie down, and open it on top of a scaly spot. Get out of the pool and watch. If it's calcium (carbonate) it will fix, and will probably remove the calcium in that spot.

Don't leave the acid sitting there more than 15 minutes -- brush it around and dissolve it, after that.