Formalin 3 can be hard to find, but Hikari Ich-X (the Saltwater version) works really well on Brooklynella. Hopefully you can find it - fast.
If your local doesn't carry it - ask them to. Everybody should have at least a small bottle of this stuff in their Fish First Aid Kit. Formalin doesn't expire so you can keep it forever.
Formalin based meds were the best 'gun' I found against Brooklynella.
Fish-Vet stuff is good too if you can find it.
Back in the early days of my shop, I got a shipment of fish sick with Vibrio and the guy at Fish Vet saved my bacon. Unfortunately the carnage was well under way by the time I found Fish-Vet and got the medicine in, but once I got it, the medication took care of business.
Jenn