Rainbow With Ulcer?

[Coomon10]

Hi guys

My rainbow has a small red blob coming from it (stomach?) this has been there for last few days and is slowly getting bigger. Please can someone let me know what they think it is and required treatment? It is still eating and active but this does not look good at all, no other fish have anything similar.

TIA



Sorry, can't seem to get any better picture than these...

 

[WILDER]

Can you describe the red blob.
Ulcers are pink or red with a white circling of dead skin around the edges.
Anti internal bacteria med by interpet.