The best way to add calcium

[Dorkel Marine 1]

ok I've put my specs for the 1 tank in the Tank Specs forum. I couldn't find room for the 2nd tank. It has about 10 lbs of live rock and a 3in. sand bed. bugs galore and a few crabs and snails. some algae is growing halimeda. The goal is to get the skimmer hooked up. Its a prism. Then I'd like to interconnect the two with a pump and some tubing still looking for some ideas on that. I'm rambling. i would like to get my calcium levels up to norm. I know water changes cannot replace the calcium. So any pointers appreciated. And pointers on how to hook the two tanks together and so on. Thanx in advance George.