I have recently observed a phenomenon in my pool that leads me to propose the following hypothesis:
SWCG scaling is caused by relatively high TA levels, whether or not the pool's chemistry is in balance.
My pool is three years old. For the first two years I experienced the commonly reported problem of calcium flakes being discharged into the pool from my SWCG. During that entire time, I kept the pool's chemistry in balance. This last year, in an attempt to get the other commonly reported problem of constantly rising pH under control, I brought my TA down to about 70-80 ppm. During that time, I did not see any discharge of calcium flakes. A week ago, in order to repair a crack, the pool was mostly drained and refilled. Due to the chemistry of my fill water, after rebalancing, my water now has lower CH and higher TA than before. Flakes galore! To those of you who understand chemistry, is there some possible reaction going on in the SWCG with "high" TA levels that leads to scaling?
Before the drain and refill (no flakes):
After the drain, refill and rebalance (lots of flakes):
pH: 7.2 (hoping to drop the TA)
CYA: ? (waiting for it to dissolve)
After a few days of the pH drifting higher (still flakes):
(the rest not retested, presumably the same)
I'm not going to do much to drop the TA any more this year, since I have only about a month of the season left and, then, our rainy season will naturally bring the TA down before next year. But, I thought I'd let you all know about this in case it might spark some insights.