I have a 30 gallon tank with 3 angel fishes over a year now and last night, I have realize that part of the angel fish upper fin was missing, it looks like something bit it off. Is there some type of bacteria that is causing this problem? Is there any suggestion to solve this problem? If theres any request of picture for this problem I would post them if requested.

Thank You.

Pics would be helpful. Also can you please answer the following questions to give us a better idea of your tank:
What size tank? How long has it been setup?
What are the water params?
Water changes? How often?
Any new fish or plants added lately?

Finrot comes to mind, but I would need more information to properly give advice.