White fungus on dwarf gourami?

Male "flame" dwarf gourami has been looking a bit peaked & acting sluggish for
a couple weeks, today I noticed a 3/8" diameter fuzzy white circular growth on
his body.

I assumed fungus, and since my malachite green / formaldahyde ich med also
indicated "for fungus" I isolated him w/ a bit of that med in the water.

I doubt that he's long for this world but,

1) does that approach seem ok? &

2) do I need to treat the rest of the tank? everyone else is pretty perky.

TIA -- Jim