After looking through online information I'm sure my 7-8 year old Black Moor has dropsy. It has become massively swollen over the last few weeks and now it's scales are pine coned up and it resembles a 'puffy fish' now. I really don't want it to suffer, I've changed the tank water and added a measured quantity of aquarium salts to my 108 litre sized tank. My only other goldfish in the tank is around 12 years old and is fine.The black moor spends most of it's time just floating on the surface in the same place in the corner of the tank. It feeds normally but struggles to get down and remain below the surface and often ends up upside down. We have had it since it was the size of a grape and nowdays it's around 5 inches long from nose to tail. Should I put it out of it's apparent misery or continue to wait and see how it gets on is my question ?????