calcium at 345 ppm

[Fish]

This doesn't answer your question about how to raise your calcium but, is there a problem with having a level of 345? (I really don't know)
I'd guess that 480 is higher than what would be found in nature. You didn't mention what corals you have or if you keep clams or heavy calcium consumers but I would suspect that a stable level is more important than a magic number. Just trying to save you some hassle and money - I might be totally wrong though

- Chad