We Have 2 Firebelly Toads. One Of The Toads Has A Fungus On It. What Should I Treat It With?

My toad tank is half of 10 gall. Aquarium and has about 6in. Of water for the toads to swim and hide and land to climb onto. There is also a small channel cat in there too. I need something to treat the toad with the fungus and not harm the other toad or the channel cat.