It's already too late if it's Brooklynella.. Sorry to say that, but I've been down this road before. It's a horrible disease. I saw my two Clowns and my Arc Eye Hawkfish die from it. It literally went from me noticing "something weird" going on in a day to full blown Brooklynella and the fish dying withing three days. I had a QT/Hospital tank set up the first night with Formalin. On a positive note I had other fish in my DT that did not get affected for one reason or another.