Yeah im not real familiar with parasites and stuff. These fish were all QT so im not sure how he got a a parasites. I tried to do things right to avoid parasites and issues like this.I don’t think this is related to water quality. The goby is very thin, more than it should be if it just went off food recently. I think that even though it was eating up to recently, there was some malabsorption problem. The two common ones are internal worms or Mycobacterium. Neither can be resolved once a fish gets this thin - sorry.
Jay