My fishy has red sore at base of the tail fin. I just noticed it today but it seems it may be a condition for a couple day now. It looks like an open cut, reddish in color. My Ryukin shares a ten gallon tank with a lionhead but the other fish is fine.
He swims and eats regularly and other than the sore he seems to be fine.

Can someone suggest a cure? Is ther something I can do for the fish ???

Tank conditions - Water params are normal. Amonia, Nitrate, Nitrites, ph all within the recommeded params by this site. 25% water change every 4 to 5 days. I was feeding just pellets but have introduced blood warms for about 2 weeks now.

good morning.
was there anything in the tank that he might have scratched himself on? or been able to get scratched during a water change? or do you think this is coming from an internal source (is it a boil type look)?

since you have noticed it, has it gotten larger? darker? any fuzzies?
do you feel that it is something you can watch for a day?

starting with the water... make sure it is indeed as you stated (within the correct params) no off ammonia, nitrites, or nitrates

recheck your tank for any scratchable surface

if you think this is something that should be treated but not critical.. then look into salt and/or melafix or a hydrogen peroxide and ointment swabbing for a lower stress treatment

if you think this is the start of a bacterial infection, because its getting worse, spreading, darkening getting whitish or fuzzy... then you'll want to use a true antibiotic. (just remember that antibiotic can ruin your cycle)

-Tooter

thanks tooter

I dont think it's because of a scratch because the wound is at the base of the tailfin where the tail meets the body and it is on the underside of the tail. Also I dont have anything in the tank except a plastic grass and gravel and marbles. So I think we can rule out scratching.

Just checked the water params and everything checked out ok but did 25% water change anyways.

I checked the wound again today and it seems that the red has gotten less. It kinda looks like when you have a cut on your finger and you let you hand sit in water for a long time.

The Hydrogen peroxide and ointment treatment looks likes something I could probably try. Would that be harmful to the fish if it is not the correct treatment. I'm afraid to cause it any more stress than it is already under. If I use ointment, what kind of ointment should I use and how often should I repeat the treatment?

Thanks for the advice.

It does sound like a cut or a scratch. Melafix would probably do wonders. My wife had a Gourami that had a chunk bitten out of him and melafix really helped get it sealed up fast.