Originally Posted by Fishyfins

could you perhaps post more details about the fish and tank? it would help us to know the following details:

size of tank:
size of fish:
how many fish are in tank:
filtered: (edit: sorry, you mention filter in the question, so im guessing the tank is filtered XD)
how long has the tank been set up:
was the tank cycled before you added the fish, if so, how:

also, if you have test results for Ammonia, NitrITE and NitrATE, they would be of great help (if you dont have a testing kit, either get a decent liquid test kit, or take the water someplace for them to test it for you and have them write down the results).

lastly, perhaps a photo of the pink patches would help.

once we know these details, we should be able to have a better undertstanding of whats going on, what they are, and what is causing it.