Sick Goldfish(Some Tumor Like Growth In Fin)

hi i have a goldfish (fantail).i recently noticed that it has some growth in the fin (pic attached ).i am not sure what to do . i have seperated it  from the pond .
details of fish  and pond :
pond size 14400 L (approx)
other fishes ( carps,an oscar , a another goldfish,pleco)
age: i am not sure , i bought it when it was about 3-4 cms about 2 years back 
size :about 12cm excluding tail .
 

It's possible that it's fungal, but with a pond of that size, I doubt it. Goldfish and similar fish are prone to certain tumors and cancers. You can try a quarantine tank with a fungus remedy, but if that doesn't help, and the fish seems to swim and act fine, I would leave it alone. If it becomes too large for the fish to swim normally, or it stops eating, you'll likely need to euthanize.