Need some advice on fin rot

[D_K]

I have a flame dwarf gourami that is having some issues that I need help with. He is in a well established 38 gallon tank with all parameters well within specs (except for water hardness that hits the double digits) thanks to dual filters and weekly water changes. A short while ago I noticed that he had a small hole in his anal fin. Well that little hole is growing. It is literally a hole with no fungus or anything else around it. He seems perfectly happy along with the rest of his tank mates. No one else is showing any issues. I was wondering if I should move him to my 10 gallon QT tank and treat him with melafix? Anyone have any suggestions?

[Lupin]

So there are no white edges on the hole as well? I'd isolate the fish, yes and do daily water changes. If there are white edges, you could try applying iodine solution on the edges with a Q-tip to disinfect from possible bacterial infection. What are your water parameters?

[D_K]

Nope, no white edges or any discoloration.

Water parameters are as follows:
PH = 7.0
Ammonia = 0ppm
Nitrite = 0ppm
Nitrate = 15ppm
KH = 12°
GH = 11°