I had a bad outbreak of ich in my system. I lost 5 Catfish and 4 bluegill. I thought all fish were dead but found a lone survivor the day after I scooped out all the dead fish. It's been several days and he's still alive though he has one white spot on him.
Should I get rid of him before getting new fish?
Well I got rid of him so I can make a fresh start.
Ah, too bad. Ich is easy to treat with salt, and the fact that you had one survivor makes him an especially tough fish, and good to have around, especially for breeding. Anyway, Ich is ever present, and will strike when conditions permit, so getting rid of the fish doesn't help the next go-'round any, sorry. Chances are, the previous outbreak allowed the critters to form cysts that lay dormant on the tank floor. As long as water chemistry is right, the next batch should be alright, but be quick to observe signs of ich or other trouble. I keep all my systems salted with 1 ppt salt (50/50 mix of NaCl and KCl) for the health of fish and plants, always. If restocking with bluegill, you should salt the water to 3-5 ppt anyway, as they are very susceptible to stress, and salt is a huge help. The change in salinity is what kills the parasites, btw, so salting the water will also help kill the free swimming ich before you restock. If you again get ich when your water is already salted, then do water changes to reduce the salinity by 2-3 ppt. If catfish will be going back in (or if salt sensitive plants are growing), then keep the total salt at 3 ppt or less.