Several months ago we moved into a beachfront house with a VERY large pool--about 33,000 gallons. I have been maintaining it. It tends to prefer a 7.8 pH, which may be the local water. I balance with occasional muriatic acid, and I use a liquid sodium hypochlorite chlorine solution. The pool maintains chlorine level pretty easily, even though it is an outdoor pool. The stabilizer level is a quite steady 100. I have been advised by the pool company where I test my pool water to add sodium bicarbonate from time to time to balance overall alkalinity. The pool is clear, balanced, and wonderful to swim in.

However, the calcium levels seem to be creeping up: it has maintained between 340 and 480, and recently jumped up to 680. The pool company is recommending Cal-Treat, but I am reluctant as the pool is very clear. There is a darkening of some of the tile around the waterline, which can't be brushed off (I brush the waterline weekly).

Advice, please?