The reason I am asking is that I am current running my 180 gallon under tap water. My tank is evaporate too much I don't have enought RO water to supply for it. Right now I only have a few coral and they seem to be hardy. They are torch coral, lether, mushroom, toastoad and zenia. I would like to have clam and some sps coral but I am not sure they can handle tap water. My tank currently run 4 of 160 watt VHO and 2 of 175 Watt metal halide. I have a refugi sump about 50 gallon and about 150 lbs live rock. I have lots of caulerpa in the sump and light 24 hrs. Any advise is greatly appreciate.