It was only last week that I had a similar problem with my one of my clawed frogs. I went out and i bought some 'melafix' which contains extract of tea tree oil which is superb for fixing the likes of ulcers and open wounds. I put in 10ml every day and do a 20% water change tokeep everything clean. If you leave the problem when it is at its bacterial stage then it will progress, more than likely to a fungal problem which will be very unpleasant.
Im no expert in this field but I can only give you advice that worked for me as my frog is fine now![]()