don't overfeed his with Ca, excess Ca is as bad as luck of it. Having said that what he is having now has nothing to do with Ca whatsoever.

that is what you need to do immediately. take him out of his enclosure asap and put him into bath with unflavoured pedyalite ( 1 part of pedyalite), 10 parts of treated water. apply original polysporin without painkillers on a wound, after place him in hospital tank on clean moist paper towels with sort of a hide, keep him as clean as can, apply polysporin 2-3 times for 2 days and see how it goes. monitor very closely for any unusual behavior.
if it is getting worse or stays the same seek experienced with frogs vet asap.

in case you don't have pedyalite and original polyporin, just get him washed out of substrate, place him in a hospital set up and go get the stuff.