I have two ryukins, one of them has a couple of tears in its tail they have been there for about 2 months, i have been keeping a close eye on it and they havent got any worse. Is this fin rot? How rapidly does it set in?...the fish is very healthy otherwise has a big tank (30 gal) its cycled and filtered correctly etc. If i added any medication now would it be worth it?

Well maybe the other ryukin could be chasing it.. I have my angels that have some ripped fins too. And if you have fin rot that is occurring on the ryukin's tail fins... then try and use Melafix. It's a great product and you'll love it. It is very fast at healing ick, fin rot, open wounds, and will help grow back the fins teared.

Also, try and use aquarium salt since it does help bring back the slime coat, and you will want that slime coat on because if your fishes don't have a slime coat, then ick and velvet stuff will grow on the scales and the fishes could die.

Also, try doing water changes every day. Small ones of course about a 5% water change. That takes out the bad stuff in the water. Including bacteria that causes fin rot.

Other than that.. do you have a heater in your tank? Goldfishes can survive in a heated tank.

if you do... put it up to 76 - 80 if you want. 80 will be warm enough to kill the bacteria in your tank and the fin rot should be able to go away