Black spot on Gouramis

[mrpessimistic]

Black spot on Gourami

I have a black spot that I'm trying to figure out what it is. Fish acts fine and it otherwise healthy. All of my other fish have no problems at all. Spot started out small and is slowly getting bigger.

 

[Delapool]

Wondering how quickly it appeared? Also if you have checked tank ammonia and nitrite?

 

[mrpessimistic]

NO2 is at or about 0. NO3 is about 30. Ammonia I need to get a new kit and havent tested in a while. I do 20% changes every week which will be tomorrow. I thought is could be ammonia burn and did a 50% change a few weeks back and have kept on top of the changes. No other fish in the tank has any problems, just this one fish.

The spot started probably a 3 months back and is very slow growing. Read somewhere it could be a bruise but its not getting any better. Fish acts perfectly normal.

 

[Delapool]

Yes would be good to close off the ammonia just in case.

So it sounds like it's been there a bit less than a month and only on one side? Definitely not natural?