White spots on my live rock - Calcium Buildup?

[pammy]

Hey all.

My tank has been up and running for 6 months. Calcium wasn't getting above 340 (Magnesium is 1200 - Salifert test kits). I wanted to avoid dosing anything so tried switched salts after about 4 months from Tropic Marin to Reef Crystals, but didn't see any increase, so finally bought some Seachem Advantage Calcium and Magnesium. I dosed the Calcium only, twice a week for two weeks (1.25 tsp for 60gallon total volume), and also at a waterchange, and calcium is now at 395 which I'm happy with. Magnesium was still at 1200, so I dosed that twice last week per instructions, but haven't retested yet. There are some whitespots in the nooks and crannies on top of some of the live rock. Almost looks like it snowed on it. Not covering it, but just pockets of it. It doesn't blow off with a turkey baster. Is this normal when you add calcium? Does it go away, or signal a problem?

Just fyi...the rest of my parameters.... Nitrites, Nitrates, Ammonia, and Phosphates all zero. PH 8.0 lights off / 8.25 lights on.
Alk is low.... 2.5 . Salinity 1.026 Temp - 80f. RO/DI water.

Also, now that I have my calcium where I want it, I know I'll probably have to probably just experiment, but are there chances I can just add a dose of calcium with waterchanges, or am I most likely going to end up dosing twice a week. I have LPS and Soft corals only. One rock with about 8 mushrooms, some zoos, sun coral, aussie duncan, 1 crocea clam, two feather dusters, 5 fish.
Tank is 53 gallons with a 7 gallon sump.

Thanks, Pam