What should you be adding? Right now, probably top-off water. Waterchanges will take care of what you've got easily. For more Scleractinian corals, you'll possibly need to supplement the "big 3" (Calcium, Bicarbonates, and Magnesium), however some crazy people (ie. me) add anywhere up to 11 different things in addition to these. Isn't needed in most tanks, except for those with very specific care requirements. Keep it simple and you'll be rewarded kindly.