I picked up some new fish "Yellow Tang, Bristletooth Tang, Melaranus Wrasse, and 2 PJ Cardinals" last weekend and have had them in the QT since bringing them home. Yesterday I noticed that the Yellow Tang has what looks like black ich. I have never dealt with this stuff before and I'm wondering how to beat it? They are all in a 45g QT tank without sand or rock so I can medicate with no problems.