If you haven't seen spots it is probably not ICH or a parasite, but maybe a scratch that has become infected and open. This may be causing the "itch". The exposed area of skin is cause for concern though. 1st thing to do is increase the water quality - water changes will lower bacteria and what feeds them. I would perform 3-4 water changes over the next 10 days or so. Also clean any filters and waste, and use carbon or a poly filter if possible to remove doc
and nitrates. Be sure the new sw
is mixed for 24hrs to aerate. Feed with a vitamin supplement as they said.
Meds are not needed for something like this - and never in the main tank. Meds are usually a bandaid for a larger problem like water quality, lack of maintenance or lack of quarantining - so meds should be a last resort only. Give it some time and care and he should recover fine.