HITH? u talking about the small pits opening up around the head? its called hole in the head disease. water xhanges and varied diet will help a lot. tons of weird info out there if u google it tho ive seen people blame everything from windex to carbon for hith.
i wouldnt bother isolating. it will heal and it looks bad, but doesnt usually effect fish too much. vitamins should help as some say it is caused by vitamin deficency from feeding the same food. my tilapia had it pretty good and never went away completely but has gone down since i stopped feeding only hikari bio gold. had the fish almost 4 years and never gone completely but seems to be a healthy fish. weirdest disease ive researched but pretty common. can get very ugly if left untreated though, check out pics on google of oscars.
You should up your water changes, gravel vacuming & filter maintenance. Keep your water as clean as possibile at all times. you can use Vita Chem or a vitamin block(s) in the tank if you want to add vitamins both work well for this.
I've been using metro. I've been doing more water changes more frequently. I also bought an additional filter and chemi pure in 2 of my eheims. Where can I buy vitamin blocks from? What should I keep my temp at? Any other input would be valuable.