If you have a reef tank , Expect to HAVE to dose calcium and alkalinity supplements. Their are a few occasions where calcium and alk consumption is low enough that water changes will keep levels higher but be sure to test your tank....jthat's the only way to know what you need to be doing. IMO, dosing Ca should be a daily thing...although they do have products that say add weekly or whatnot, daily just seems to be better...more consistant.