I've tried the test kit from Jack's Magic, and it did not definitively remove the scale. The scale just appeared over the winter in my mesh covered (formerly white) plaster pool. All the chemicals and chlorine are balanced. The pH was a bit low when I uncovered and it didn't take much chemical to resolve that. The water is nearly crystal clear. I'm using a sand filter and keeping the pump on 4-5 hours a day to keep the chlorine up.

The pool is fine otherwise. I'm in Austin and it's 100F everyday. Is it getting revenge on me for covering during the winter?