were the snails, crabs, and blenny quarantined? how long?
brooklynella is a fast killer (so is velvet) and you must act immediately. remove all of the fish into the quarantine tank right after you get off work and dose the med (either quick cure or rid-ich). if you have trouble distinguishing between velvet and brooklynella, take a white LED flashlight and shine on the fish. brooklynella films tend to be white and velvet usually has a light gold sheen to it. having a dark background will also help.
Once you are fairly sure which parasite you have, dose the med right away. Do still post a picture so we could all look at and comment, but don't wait for us as either parasite kills very fast especially when the symptoms are present already.
Unfortunately the new fish, crabs and snails were not quarantined before I put them in my tank

If it's velvet use Cupramine. 0.25ppm is high enough to kill velvet so just do one dose of that.