When I have a sensitive finicky eater type fish I was putting them in my 29g refugium, which is full of rocks and macroalgae & fishless except for a mandarin. Now I have a separate 29g algae tank. It's packed full of algae & pods & has some rocks to hide in + the additional advantage of being a separate system.
I wouldn't treat a fish unless it showed specific signs of an illness. Then , if possible, I'd give it oral medicine either by soaking the food or gut loading some live brine. I don't really have much experience with dips or copper - but often a more sensitive fish can't take that sort of treatment anyway. As far as what fatheads can tolerate specifically, I'm afraid I don't know.
I did look up fathead grouping and S.Michael says that when found in shallower waters they occur as 1-3, but deeper they do occur in larger groups. He hypothesizes that since they are more abundant in deeper waters it may be easier for them to find enough fish to get a larger group together.
They do have specific habitats that they are found in - near caves/hiding places along verticle drop offs, dimly lit waters. S.Michael Vol 1 has more info
