Method
Put a heater in one of the small tanks and add 4.5 litres (1gallon), no more, no less, of your 25ppt water in and bring it to the same temp as the QT. Add 2ml of the Interpet Anti-Parasite, measure this EXACTLY from the syringe. Next get the aeration going full speed, the more aeration the better. Leave this for a minute or two to spread the remedy fully throughout the water.
Net the fish and place it gently in to the formaldehyde bath, cover the bath and set your mobile phone, or other, alarm for one hour. Watch the fish carefully for signs of distress. If showing distress, immediately prepare the rinse bath, see below, and remove the fish
While the fish is in the bath and showing no signs of distress, completely strip the quarantine tank and clean the tank, the heater, air line and air stones thoroughly . When done setup the QT again and fill it with your new 25ppt water, don't forget to switch the heater back on.
When the time is almost up get the 2nd small tank and add some of your 25ppt mixed water, enough so the fish fits in comfortably, this is your rinse bath. When the alarm goes off immediately net the fish in to the rinse for 5 minutes, don't worry about aeration or heat, the fish won't be in there long enough to cuase problems. Rinse your catch net under the tap and flick out any excess water. After 5 minutes net him and put him back into the QT. Discard the entire contents of the formaldehyde bath and rinse the tank, heater, air line and air stone in fresh tap water.
Repeat this bath procedure no earlier than, and as close to 24 hours after the previous bath. To make sure that Brookynella Hostillis has been eliminated you need to give the fish 1 x 1 hour bath per day to a total 5 baths.
Add a broad spectrum anti bacterial remedy, to the QT to avoid any secondary infection as a result of the broken skin the Brookynella Hostillis parasite causes as it leaves the fish.
Keep the fish in QT for a week after the last formaldehyde bath anti-bacterial remedy you choose has run it's full course as directed by the manufacturer. And keep up the 50% daily water changes. Remember to dose the new incoming water volume, not the whole tank volume, with the correct amount of your antibacterial remedy at every change.
After this week was up I transferred the fish to a Recovery Tank, a Aqua-One AR126 in this case, which had full filtration.
Notes: Make sure you have plenty of 25ppt water mixed and ready to go everyday.
Formaldehyde is nasty stuff, use it in well ventilated areas and always, always read the manufacturers safety instruction on the bottle.
Formaldehyde drives off oxygen so remember to keep the water well aerated when the fish is in the bath.
Extreme Caution: Never, ever be tempted to add Formaldehyde at 200ppm to your reef tank or any system containing Live Rock. Most, if not all, life in the system WILL be destroyed