Red Streaks On Goldfish Fins

[BettaBubble]

Hello! I have a fancy goldfish who has red streaks in his tail fin. Would a simple water change help? None of the other fish have it. Is it serious?
Tank info:
I have 3 fancy goldfish in a 55 gallon aquarium
Last water change was last week.
Sorry I don't have the water perameters, I ran out of the tests. I am going to the store asap.
Thank you!

 

[emmysjj]

Is the tank cycled?
Pictures would help

 

[Lorekeeper]

How new is he?

Sometimes, red streaks are just natural coloration. If it's more of a veiny appearance, I'd suspect stress. Goldfish can get some red vains showing in their fins after shipping or stress, so I'd suspect that if he's new.

 

[BettaBubble]

Yes the tank is cycled, Ive had it for about 1 year. He is 6-7 years old and ive had him basically since he was a baby. Unfortunately my other fish ate most of his tail off. I feel so bad. I never noticed any aggression before, and it all seemed to happen over night. One day he had the tail and the next he didn't. I rehomed the aggressive fish the next day. Is there anything I can do to help it grow back faster? I feel horrible that I didn't notice anything before. He can still swim but just a little bit slower. I can post a picture if you still need it, tomorrow.
Thank you for all the help