Your water perimeters aren't "good" if your only stock is 2-4 feeder fish and 2 ID Sharks that appear to be no more than 3" long and your nitrates are reading between 40-80ppm. That's HIGH. When is the last time you performed a wc?
Your biological filter isn't still establishing itself if your reading 0 amm, nitrites, and a read on nitrates. Your cycle is complete.
If your heart isn't in FW I guess I'm just kind of confused as to why you just picked up two ID Sharks. You do realize they grow fast, require huge aquariums at full adult size, can grow over 3' long, and can easily live over 10yr if properly cared for. (Which practically never happens with these poor guys)
As far as treating the odd looking issue they have going on around there mouth, first thing I do when I have any health issues with my fish is check water conditions. If nitrates are over 10ppm I'll perform wc to bring the nitrates down below 10ppm and keep it that way with wc. If there are no improved results with the water quality resolved I would move onto either meds, or salt dose w/ temp bump depending on the issue.