My sailfin tang used to be very active but about a week after I added a flame angel he has started to sit around a rock at the bottom of the tank. The flame angel is quite active but has a white spot on its gill and I thought I saw it flick against a rock. There is a yellow hawaiian tang, a firefish, watchman goby and percula clown in the tank also...they are still active with no signs of illness. My water params are great ( 0 ammonia and nitrite, very low nitrates, 1.024 salinity) I am worried it is ick. What is the best treatment for ick (which brand is the best), how should my (25 gallon) sick tank be set up (I know no substrate but can they have rocks to hide in, what filter should I use...), and how can I be sure the cured fish wont get another infection after being put back in my display tank since I can't use treatment in there because I have corals and inverts?