Black Residue On Goldie?

[GouramiGirl87]

My goldfish's fins have been clamping up within the last few days, and now has produced this black residue type substance on his head. He's in a 20 gallon tank, I'm bringing in water later on today to figure out the levels etc. any help is greatly appreciated. I should note, yes he is in 75 degree water, but that's pretty much room temp, with a tiny bit of heater to keep the temp stable since my tank is by a window. His tank mates are two dwarf gouramis and a chinese algae eater. My tank has been up for two months.
THANKS!

 

[The-Wolf]

I've had fish with this problem at work
we treated with acriflavin (NT labs) at the dose of 1ml per 30ltr
for 5 consecutive days. all of them were cured.

HTH

edit I just noticed that you are in the USA
acriflavin is an anti-bacterial, but a very strong one.
I'm not sure it is available over there;
get the strongest that you can.

 

[WILDER]

Something like tetracycline, but it will wipe the bacterial colony out a far bit, so it would be better if you could issolate the fish for treatment.