Odd Fin Disease

[Shummy]

I have two standard fantails, both less than a year old. Ever since shortly after I got them they've had a black growth on their tail fins. Suddenly it has gotten worse with no apparent trigger and has slit their tails entirely where the two tails connect, but it is not affecting any other fins or areas of the tail. I don't have any idea how to treat it or what it is, help?

I can' get a good picture

 

[silverrabbit]

How do you clean/maintain your tank and filtration (assuming you have one...), what size is your tank in litres/gallons, and do you know what your water stats are?

To me, it sounds like finrot, but the sound of the blackness could indicate healing ammonia burns. If they are ammonia burns, it means that your tank is not filtered and the fish are being exposed to their waste and becoming poisoned by it.

Those details I mentioned above will help a lot and pleeease try for a pic - it helps sooo much!

 

[vfg10]

I agree sounds like amonia burns

 

[Tokis-Phoenix]

Blackness on finrot affected area's can also be indicative of poor/very slow healing (i once adopted an opaline gourami with exactly the same symptoms as your oranda's, one day the black growth affected area on its tail just fell off, however after medication and regular water changes the affected area quickly healed back). Some more info on your situation would be useful- what sort of tank maintenance regime do you have, how large is the tank and are you keeping any other fish in the tank?