Whatever you do, never use malchite green on lawnmower blenny or sandsifting goby. It completely wigged them out and killed them. I have to assume it was that since I have witnessed formalin to not be an issue and they were not ill. They were just unfortunate enough to be in the tank with 4 fish with Brooklynella and got treated too. They both died horribly. I mean, really wigged out and nothing I could do about it. Very bad experience, but I had never heard of an issue before.