I am looking at starting to add corals, so I took my water down to my lfs to test for calcium. They said it was 500. I've never dosed with anything (I try to stay away from chemicals). Is there a way to bring it down and how do I keep it from getting that high? Isn't ideal 400-450? Is 500 too high? I'm looking at keeping leathers and maybe some mushrooms. I do weekly water changes of about 10 gallons. All readings 0, ph 8.3.