Thanks blondenaso... the sps frags I have are between about 3 and 7 months old, and I have seen many different growth rates. I have two types of Montipora digitata which has grown relatively fast, and three types of plating montipora that is also growing well. I have four different acros, and there growth generally has been relatively slow, yet one is really starting to take off. However, I am in no rush and prefer a slower growth rate in such a small tank. If I had the option, I would go with a halide, but my tank is evidence that sps and clams can do well under PC and the right conditions.
As for calcium, originally I started with just B-ionic. I was tentative about dosing kalk on such a small tank. After like three months though, I think around October or November, the tank was using up way too much calcium to be replenished by B-ionic alone, and my pH was dropping a little too low at night. I then started dosing kalk at night, and started with 1/2 teaspoon per gallon, dripping about a half gallon a night in the tank. I slowly worked up to full strength kalk, 1 teaspoon per gallon. This went well for a while, but my pH was running higher than I would like, so I dropped back down to 3/4 teaspoon per gallon. About a month and a half ago my calcium started dropping below 400, and so I started dosing B-ionic on top of the kalk, and now test weekly my alk and calcium, altering B-ionic doses to keep the tank between 400 and 450 on the calcium side and the alk between 3.0 and 3.5 meq/L. My pH monitor has been crucial throughout, and I highly recommend them. I can now pretty much tell my alkalinity within .25 just by my pH swings on the tank.
Also I have tested for magnesium and have always been good there. My weekly water changes replace everything else. Anyway, here's a pic of one of my encrusting montiporas that's a gorgeous yellow...