African Clawed Frog Problem

[Captain Neon]

I have a 150 litre tank that houses two albino African Clawed Frogs- one male, one female. Both are about a year old, and generally healthy, eating a diet of bloodworm, chopped fish and chopped mussels, which they both eat avidly. Just last week, I noticed a small lump on the male, located just to the right of where his tail would be if he were a tadpole, on the top half of his body. Over the week, it's gone from being a small pimply shape to a larger diameter lump, about 4mm across and 2mm high. There's no discolouration or redness there, and his movements and feeding show no signs of difficulty or distress. Does anyone have an idea as to what this is??

 

[Captain Neon]

*update* I have added 'Interpet Aquarium Treatment 9- Anti Internal Bacteria' in accordance with the instructions, and after two doses, the lump has gone down in height, and now looks like knotted scar tissue, as if it is a healing open wound. The frog is still spirited and moving around, but he's not feeding as well now- and my recent attempt at hand-feeding him some bloodworm via a pipette (Which I can do easily with the female frog) has resulted in failure- he isn't interested in eating at all. Is there anything else I can do? I put him temporarily into a small bowl to make feeding him easier, and I discovered small organisms simming in the water, one of which was hovering near his wound. I've taken one out of the water to have a look at. It's black, looks a little bit like daphnia, but it's much smaller. Is this a parasite, and if so, how do I eradicate them?