[daniella3d]

If you did not add anything for months then it is not marine velvet.

However it could be some bacterial infection.

Discus plague is caused by a nasty bacteria that can be present on some fish and kill any new fish coming in contact with it that are not immune to it.

If we think about the flesh eating bacteria, it is present in our environment yet for no apparent reason it can start eating people flesh.

Maybe when you put your clownfish back into your tank it cought some bacterial infection and that spreaded to other fish?

I cannot be marine velvet if you did not add anything to your tank.

Does not make sense in deed.

When my discus cought the discus plague, they were covered with a white powdery looking film. Some were floating on the side half dead. I had to treat them with potassium permaganate baths each day for 4 hours at a very critical dosage and they all survived, but I was very tired by the end of that week. All this for a bacterial infection that became very potent very fast.