Some antibiotics can have adverse affects on seahorses and are recommended as a last resort only. Before you medicate any seahorse ensure you are treating them with an appropriate medication and adhere to the dose rates stated on the packet. Always medicate in a hospital tank - never treat your whole tank (unless absolutely necessary) as you can damage your bio filter or harm other tank inhabitants.
Fresh water baths (for approximately 2-4 minutes) as a treatment for bacterial and parasite problems should always be the first treatment. De-chlorinated fresh water, (to ease the stress ensure the temp and pH of the water is the same as the water they have just come from) an added airline and something to hitch to also help with stress.
Fresh water baths are sometimes used before adding new seahorses to an established tank. The fresh water should immediately kill most seawater parasites.
Topical treatments such as diluted Betadine can be used for any external lesions or sores (skin rot), a dip of the affected area, after a freshwater bath, in a 1:5 Betadine/water solution (Active ingredient Povidone-Iodine w/v 10%). If you are treating an area of the head, do not dip the seahorse, but apply with a cotton bud.
For more serious internal bacterial infections or internal parasites a Formalin (37% Formaldehyde) bath at 200 ppm (1 ml per 5 liters of sea water) will assist. Horses can be bathed in this treatment for up to 1 hour, but be sure to add aeration and hitching posts. If your Formalin contains white sediment in the bottle, do not use.
Be aware that Formalin is harmful, ensure you use with care (use gloves and do not pour down sink or septic systems when finished). A clean plastic bucket will be an adequate hospital tank for the bath.
It is a good idea to isolate any seahorse in a hospital tank if you think there is a problem, this lessens the risk for your other tank inhabitants. It is recommended to only ever add medications to a hospital tank that contains no filtration.
Male seahorses can get air bubbles in their pouch, especially when there are fine bubbles in the tank (sometimes created by air-stones - so we do not recommend the use of air stones). These bubbles will cause him to float sideways on the surface of the tank. He is probably unlikely to be able to swim to the bottom of the tank and feeding activity will be hindered, as is locomotion, this will cause stress.
Ensuring you have cleaned your hands by running them under tap water for several minutes (no soap!). Hold your seahorse in your hand while still keeping him submerged. Let him hitch his tail onto your fingers. Using your thumb and first finger gently massage the pouch working slowly from the base to the opening. You should see the air escape from his pouch opening
Try a gentle massage each day until he is upright and swimming happily again. If after two days he is still floating you will need to open his pouch to release the air.
Holding him the same as before and ensuring he is totally submerged get a blunt slender object and ensure it is clean and sterilized (a bobby pin with a plastic end can be used) and insert into the pouch carefully. You should see the air as it escapes. Do not poke the bobby pin in too deep, you may damage him internally, the idea is to just get the pouch opening to open slightly.
You may have to do this over several days as well. Once all the air is released his behavior will return to normal.