Sorry to hear you already lost one frog.

One more suggestion that might help with wounds is some aquarium salt added to the water. I add 1 teaspoon of salt per gallon of water, making sure to use actual water volume and not the tank's gross volume (in other words counting for water displacement from gravel and decorations.) I prefer to use true marine salt such as Instant Ocean instead of "aquarium" salt in the freshwater section. The marine salt is actually a mixture of several different salts and trace elements. Whereas the freshwater aquarium salt is just sodium chloride.

One more question comes to mind. Do you use a power filter? If you do, are the intakes covered with a sponge?