It took me a year to really get good coralline growth since I started off with mostly base rock...and only a couple of small pieces of live rock. Once it starts growing fast, it's hard to keep the tank clean. I scrape all glass about once a week with a razor blade...and then run a magnet across it every day or two. If you're not letting it grow, it won't suck the Ca up as fast.
I also have 3 urchins that eat the coralline...so they're covering the rocks while I cover the glass.
Just from coralline though...that's a lot of Ca to be losing. Unless you have a lot of SPS (which I don't recall you having), that's probably too high of a loss. What's your Mag & Alk?