Or you can do what i did after searching and searching endless web site, and forums, i found at DIY calcium reactor with out the Co2 which is the part that more expensive, it is basically the same principle the only different is that you have to get a strong pump more thn 700gph , ok here is how my goes i just when to lowes go a 18 inches of 3inch pvc pipe, got a 3 inch cap and a 3inch screw in cap, put it together and on the top of the 3 inch cap drill ar 1/4 inch hole or bigger you decide, got me a 1/4 elbow and glue it to the hole, and on the bottom cao drill a 1/2 hole for you pump, put a spacer on the bottom with a filter and fill the pipe with cruss coral, screw in you cap and star you pump.
Ok basically when you pump pressure water with out Co2 the crush coral with time will star to dissolve that the calcium will flow out like i said i take some time but my tank has been running for 8 month i have never added any calcium acutally MY BIGGES problem is getting my calcium down right know is something around 490 to 500 i know that is high but my fish and coral are loving it, NO MY PUMP Thought, hope it helps