I should have said the bio wheel is to be placed in your main tank to get loaded and then move it to qt from there . After looking with fresh eyes this am I would say it is vibro, it is my understanding that this is contagious , and almost always fatal if not treated ,Your horse will probably be in qt for up to 2 months if not longer .
The best treatment for bacterial infections is always preventative quarantine, but if an infection is present in the tank, hospitalization of the infected specimens and treatment with antibacterial agents is the only solution.
Combination drugs such as Furan II and Paragon II
are often most effective at combating bacterial infections. These drugs cover both spectrums of bacteria (gram+ and gram-), and can usually halt progression within days. Use the marine dose per the manufacturer's instructions. Drugs from the tetracycline family may also be of some help, specifically doxycycline and oxytetracycline,
though they may be somewhat difficult to get a hold of. Topical treatments such as neomycin (Neosporin) and iodine or formalin solutions (1 cup water to 15 drops of either or both) used three to four times daily on the affected area can also help in controlling the progression of the disease.
Advances are being made in the way of creating seahorse vaccines that could possibly eliminate the occurrence of infections of this type. The most likely causative agent in most cases is Vibrio sp., a bacterium with high resistance to most drugs available to hobbyists and institutions alike.
If the disease returns, the infected horses will need to be requarantined, the display tank may have to be scrubbed down, and all equipment may have to be sterilized with bleach. Be careful not to allow any sterilization chemicals to make their way back into the aquarium as this will destroy the essential denitrifying bacteria present in the aquarium's bacterial filter bed. If this does not arrest the occurrence of flesh-eating bacteria, the seahorses may have to be relocated to a new display system.
Contact a local vet for these meds if you can not get them at your LFS
I fortunatuly never had to deal with diseases like the above but I did research and made my own refrence library ...Your best bet is to get logged on to seahorses.org and ask them there are breeders and others there who have dealt with this and other diseases ...