that is velvet, bring all of the fish in your tank to a medacated tank as soon as possible one with copper, i lost every single fish in my tank to velvet in one week, they died one after another.... take them to copper before they all die out like mine did and then let the tank cycle for a 2-4 weeks.......and yea it isnt good to use one of your own tanks for copper treatment, i would check and see if a local LFS store carrys a copper based tank