The gramma was hiding for a week before death, the clown looked like it had brook, (whole slime hanging off its body, & im not sure about blenny. These fish also died after I added a skimmer but I’m thinking that’s just coincidence? & no extra aeration
It could be Brooklynella, all of those fish can get that. Tough to cure though - formalin works best, but it is toxic to people and hard to source. Ruby Reef Rally Pro sometimes works, but in cases where fish have already died from the disease, it often just isn't strong enough to stop the infection.
