Tail of fish damaged? Photo attached

[DoopDoopBiscuit]

Hi can anyone give advice on my goldfish. It seems to have a damaged/bleeding tail I think? Only since this morning. It seems OK in itself otherwise.

Any advice? Many thanks

Looks like a classic case of fin rot. Get yourself some fin rot treatment from a reputable fish store.

It's a bacterial infection that's often brought on by environmental factors.

What size tank is this fish in?
How regularly do you change the water?
What filter do you have on the tank?
Other fish in the tank?

Thank you. I'm not sure on the tank size I will have to check. There's 2 fish in there and they're almost 7 years old. I will get fin rot treatment, many thanks