Ummm....Have you noticed any aggressive behavior in the fish? My bet would be the clown, but that is just a guess. As for the freshwater dip, it might be a quick fix. The royal gramma may continue to get picked on which can lead to stress which leads to secondary infections. A qt does not have to be expensive 10 gallon tank or rubbermaid tote, a heater (but since it's summer you MAY be able to maintain a stable temp the same as your DT without one), & HOB filter. Use water from the dt and let the filter cartridge soak in the dt overnight and there is a qt.