Help Sick Cory

Hi I'm hoping someone out there can offer some advice. I have a pepper cory with a large sore on his gill cover. I'm not sure but I think his gills maybe exposed. I've tried using anti internal bacteria med (for open sores/ulcers) twice and it hasnt made a difference. He feeds well and swims normally, but he's been like this for a few weeks now and I dont want him to die!
Oh and none of the other corys or gouramis show any signs of illness. The tank is 14 gallons (3ftx18"x1ft) roughly! We've had the tank for several years losing and adding fish as we go along. We've had the 3 corys about 6mths. We also have 4 gouramis and 3 mountain minnows. One of the gouramis had an ulcer, but we treated it with the above meds and it cleared up straight away. The ammonia, nitrate and nitrite levels are low (last test) and the pH is high (8) as we have lots of plants. Temp is 26/27oC (79-81oF). Hope this info helps!

We really need more information to be able to help you. A clear photo would help. If they all come out fuzzy use macro mode - the one with the flower.

Water stats (ammonia/nitrite/nitrate/pH/temperature) would be very helpful.
How big is the tank and what else is in it. How long has it been set up and did you cycle it. How long have you had the affected fish?
What does the sore look like? Is it red or white? Is there anything whitish or grey or slimy around the edges of it? Is it growing and are there any signs at all that it might be starting to heal?

Corys are prone to disease and if theres a bug in the tank...they will catch it.

It looks like there is white stuff on him aswell..

Lots of water changes will help a lot. Pristine water will keep infections down and help the healing process. I would suggest daily water changes till it heals.

Wow thats nasty.
Can you post water stats please in ammonia, nitrite, nitrate, and ph.
Any signs of flicking and rubbing.
Has he tore his gills on anything sharp in the tank.

How long did you use the anti internal bacteria med by interpet.
Over the counter meds only work on mild bacterial infections.

Fungus grows on dead tissue.