That disease is terrible. Both of my clownfish had gotten it after I fed them a new bag of frozen shrimp even though my tank was healthy....within 48 hours they died.
Formalin is the preferred medication for treating brooklynellosis, and may be used on the aquarium fish either as a dip or a continual bath. “Saturated formalin” is used, a 37 to 40 percent solution of formaldehyde in water.
Formalin will kill saltwater aquarium invertebrates and algae, so it cannot be used in a reef aquarium. Formalin also displaces oxygen from water, so supplementary aeration of the water will be required in the quarantine aquarium.
This quote comes from Fish Channel, and I agree it's the best method, however anyone else's input i also very helpful:
"Treatment dips are normally performed daily for 5 days. Dosage, duration and frequency should be described by the manufacturer and may vary slightly between brands. But the required concentration of formalin is 200 mg
/l, or 2 ml of 37 to 40 percent formalin per 2.6 gallons (10 liters) of seawater. Treatment dips last 30 to 60 minutes, though the aquarium fish should be removed immediately should it show signs of severe distress, such as rolling onto its side. Some aquarium fish react negatively to formalin dips (including surgeonfish, tangs and butterflyfish), in which case half-doses should be used instead. Once dipped, the aquarium fish should be placed in the quarantine aquarium and observed.
If used as a continual bath, formalin needs to be added to the quarantine aquarium at the dose recommended by the manufacturer. The aquarium fish will need to be held in the aquarium for at least 7 days. Reduced salinity (hyposalinity) is beneficial, but otherwise environmental parameters, particularly pH and temperature, should be similar to those of the display aquarium.
Because brooklynellosis causes damage to the skin, there is value to using medications that boost or replace the slime coat of the aquarium fish after the formalin treatment is concluded. Damage to the skin may allow secondary infections to develop, so the use of a broad spectrum antibiotic in the quarantine tank is useful, especially following severe infections."
This is one of those nasty parasitic infections..... unfortunately quarantine is the best on truly only viable solution if you have corals. I wish you the best of luck in treatment and continue to keep an eye on your other fish for signs of it showing up since it is aggressive and can kill fish in a few days.