It sounds like you have been using too much of the medication, sir. The instructions call for you to perform a 50% water change daily and then to replace 50% of the antibiotics after that daily water change; it sounds like you have been performing two water changes daily and replacing 50% of the antibiotics after each water change, which would result in too much of the medication accumulating in the treatment tank over time. That can be hard on the seahorse’s kidneys and system in general.
So, if that is indeed the case, Tom, I would recommend that you perform a 100% water change as soon as possible to remove all of the medication (do not redose the tank after changing all of the water). Just give your seahorse a break from the medications for the next two or three days to allow him to flush all of the antibiotics out of his system. Continue to perform a 50% water change each day as usual, in order to maintain good water quality and prevent ammonia spikes, but don’t add any of the medication. If your pony has been getting an overdose, just let him clean the medications out of his system over the next 2 to 3 days to see if he perks up.
After he has cleansed the neomycin and triple sulfa out of his system, Tom, you can consider trying another antibiotic, if you wish. In that case, kanamycin sulfate is the antibiotic I would recommend.
Kanamycin sulfate is a potent aminoglycoside antibiotic that is absorbed very well through the skin and gills of the fish, allowing it to attack the infection internally, from the inside out, even if the seahorse is no longer eating:
This is a potent broad-spectrum, gram+/gram- aminogylcoside antibiotic. It is wonderfully effective for aquarium use because it is one of the few antibiotics that dissolves well in saltwater and that is readily absorbed through the skin of the fish. That makes it the treatment of choice for treating many bacterial infections in seahorses. Like other gram-negative antibiotics, it will destroy your biofiltration and should be used in a hospital tank only.
If I could only keep one antibiotic in my fishroom medicine cabinet, kanamycin sulfate is the one I would choose because of its excellent solubility in saltwater and effective absorption.
Best of all, kanamycin sulfate can be safely combined with certain other antibiotics such as doxycycline or neomycin or triple sulfa to increase its efficacy, as explained below. If you can keep more than one antibiotic in your fishroom, make it one of the antibiotics that can be combined safely with kanamycin to produce a synergistic effect. For example, kanamycin + doxycycline is an effective combination for treating certain Vibrio infections. Likewise, combining an aminoglycoside antibiotic (e.g., kanamycin or neomycin) with triple sulfa works well for combating some bacterial infections in seahorses.
In this case, the kanamycin may be even more effective if you combine it with triple sulfa. The triple sulfa attacks the infection from the outside, while the kanamycin will be absorbed into the bloodstream, where it can attack the infection from the inside.
You may be able to find a medication that includes kanamycin as its primary ingredient at one of your local fish stores. Or you can always obtain pure kanamycin sulfate powder without a prescription from National Fish Pharmaceuticals at the following URL:
best of luck resolving this tail infection, Tom.