My calcium was around 600, snails rock corals ect all suck up calcium , your only over dosing when you get a white cloudy film,even though 400 ppm is optimal range for natural sea water but being to high wont kill anything as long as theres stuff in your tank that will suck up the calcium, when your alk is stabalized your Golden..I stoped dosing when my calcium was at 600 , wrong thing to do, evrything was doing fine untill then , but i read to much , and listened to too many peoples advice, purpline alage stoped growing and i lost 2 corals , started back the original way corals never looked that good it took a couple of months for my calcium to come down, but when it did my alk was nearlly perfect range also, they go hand in hand,if your losing corals do a water change...