I recently bought a used calcium reactor. It has some media in it but how can you tell if it is used up? Does it melt completely away or what? What kind of media can someone recommend? I also heard about mag. rocks, do they work good and what type would someone recommend. I have a 125gal. and recently bought a 140gal. I would like to run them together with a 30gal. frag tank. any advise is greatly appreciated. I'm not sure what size tank the reactor is rated for but it is pretty big. (one chamber 20" high and 8" in diameter, runs on a mag 5)