the ammonia/nitrItes/nitrAtes are all at 0, I have corals... and everythings fine.... I dont know how to get the cal. down I tried a water change and that didnt work really its a 20L gl and I know those are a little harder to keep stable... what can I do to get the cal. down? other then the water change.... I'm scared if I do another change it will mess everything else up.