Whats Wrong With My Sterba

Hi Guys, I need a bit of advice. Just looking at all the guys in the tank today and noticed this grey dis-colouration on one of the Sterba Corys just in front of his dorsal fin. When taking it out of the water it is un-noticable, however there is a large yellow/green lump that has grown behind his right eye. Can i keep it in the tank? Is it contagious? Any advice welcome. Had a pair of them for a week and a half and the other one is fine. There are about 8 other corys in the tank and they are fine. Ammonia is zero, Nitrite is zero, and Nitrate is 40ppm. i'm doing 20% water changes every week, and the last change was yesterday. Temperature and PH is all ok. I've attached photos. It is behaving normally as well

If you have an hospital tank I would isolate him.
Any signs of flicking and rubbing.
Is the lump behind the lens of the eye.
Is the lump on top of the eye, if so does it look hard, or soft like filled with fluid.
Does the lump resemble a cauliflower.

Is the grey colouration spreading. Like to forming a saddle shape on the fish.

Its a strange one. The fish is acting naturally as ever. No rubbing against anything. My mate who shows fish thinks it might have a secondary infection as the left pectoral fin seeems to have been broken. Couldn't really explain the lumps on the head though. They seem a bit like blisters as the skin seems to be stretched. Its currently isolated and has had a bit of Melafix added to the water. I'll be keeping an eye on the tank floor to see if any of the other fish are harassing any of the others. This may explain how he got a broken fin

Chris

Forget melafix it's only good on cuts and wounds.

I would try a bacterial med. What's your location?