I've been there trying to balance calcium and buffer. Its a pain having it bounce back and forth. I'm sure my corals and other critters don't care for it very much either. I think you also get an initial spike in calcium from the dissolution of sand my bacteria colonizing the sand bed. Unfortunately, the buffer gets used up by the acids produced by the bacteria as well. That's what causes the imbalance. Don't ask me to prove it, its just a pet theory.