Try dipping tail in melafix. Will help it heal.
Other options would be neomycin + triple sulfa for at least 14 days. Like neomycin sulfate, kanamycin sulfate is an aminoglycoside antibiotic and the two can be combined together and safely used with triple sulfa, so that is something you might consider.
Last option is Debride Medicated Ointment to the skinned area of the tail will help the seahorse to feel much better. The medicated ointment contains a topical anesthetic that will numb and soothe the affected areas, whereas the corticosteroids will reduce any swelling or inflammation on the seahorse. If you can't find Debride Medicated Ointment locally, then you could disinfect the skinned areas of the seahorse’s tail using a good topical antiseptic such as povidone iodine (brand name Betadine), which you can obtain over-the-counter at any drugstore or pharmacy.
You will have to though, remove the affected seahorse from the water briefly. To prepare for this procedure, you will need to lay out a stack of paper towels in your work area, along with the iodine or Betadine and a small cup of aquarium water from the seahorse tank. When you are ready to proceed, cup the stallion in the palm of your non-dominate hand and allow him to wrap his tail around your fingers so that he feels secure. When the stallion has a good grip on one of more of your fingers in such a way that the reddish spot is readily exposed and easily accessible, lift him out of the aquarium and hold him over the stack of paper towels in the upright position, with his head higher than his tail.
Then dribble the Betadine antiseptic liberally over the open wounds and injured areas of the seahorse’s tail using your dominant hand (or have a helper standing by to carefully apply the antiseptic while you hold the pony), being very careful not to let any of it get into the cup of aquarium water or to come in contact with the fish’s gills, eyes, or mouth. The idea is to dribble the antiseptic over the injured areas from a short distance above the suspicious spot without actually touching the skin or contacting the seahorse with any sort of a swab or applicator.
The povidone iodine (brand name Betadine) kills germs on contact, so it will disinfect the affected area within moments. Just wait 5-10 seconds for the excess Betadine to drip onto the stack of paper towels, and then immerse the tail of the seahorse in the cup of aquarium water two or three times – keeping the seahorses head out of the cup of water while you do so – in order to rinse off the excess Betadine, and immediately release the seahorse back into the main tank.
It’s a simple procedure, which should take no more than 30-60 seconds, and is completely noninvasive so there should be a minimum of stress on the seahorse. If the seahorse tolerates the handling and disinfecting process well, you can repeat these topical treatments daily if necessary.
