The active ingredients in Furan 2 consist of two nitrofuran antibiotics (nitrofurazone and furazolidone) plus good old methylene blue. The usual dosage I have seen for this product is one capsule per 10 gallons of water, but nitrofuran antibiotics are only helpful for mild skin infections when used as a bath.
Furthermore, you have to take special precautions when administering nitrofuran antibiotics because they are photosensitive and can be deactivated by light. That means you’ll need to darken the hospital tank while you treat the seahorse. Do not use a light on your hospital tank, cover the sides of the tank with black construction paper or something similar, and keep an opaque lid or cover on the aquarium during the treatments. Remove this cover from the aquarium only long enough to feed your seahorse.
If you suspect your seahorses have a serious systemic infection (Vibrio) rather than a superficial skin infection, then you must administer nitrofuran antibiotics orally via bioencapsulation in feeder shrimp or it will be ineffective.
However, in the case of a suspected Vibrio infection, I would recommend treating your seahorses with kanamycin as a bath, or tetracycline or oxytetracycline administered orally.
Kanamycin dissolves well and is very stable in saltwater, and is one of few antibiotics that is absorbed well through the skin and gills of saltwater fish, making it the treatment of choice.
Tetracycline antibiotics, on the other hand, are useless when added to saltwater and used as baths. Tetracycline and oxytetracycline bind with magnesium and calcium, rendering them inactive and making these medications useless in saltwater. Tetracycline antibiotics are nonetheless quite effective when administered orally, since the medication gets into the bloodstream when ingested without being deactivated by the magnesium and calcium salts in seawater.
Also, since your seahorse still has a gas bubble or subcutaneous emphysema on its abdomen, I would continue treating the affected seahorse with Diamox as well. Since the seahorses still eating well, I would try treating it with full-strength kanamycin in a hospital tank for 5-10 days while you administer Diamox orally once a day as discussed below.
I would suggest injecting feeder shrimp with a Diamox solution and administering the medication orally in this way, rather than removing your Sunburst to a hospital tank for another series of Diamox baths.
If you can obtain a small syringe with a fine needle, the acetazolamide solution can simply be injected into feeder shrimp or even frozen Mysis. Mic Payne (Seahorse Sanctuary) used this method of administering Diamox successfully when he had recurring problems with GBD due to maintaining a population of Hippocampus subelongatus in shallow tanks only 16-inches (40 cm) deep:
"Seahorses maintained in this system are susceptible to gas bubble disease. Specimens with bubbles around the eyes or under the epidermis of the tail are readily treated with acetazolamide (Diamox tablets 250 mg). Mix a very small amount of crushed tablet with water and inject it into several glass shrimp that are then frozen. These are then fed to the target animal at the rate of two per day for four days. Bubbles disappear on the second day."
Volcano shrimp or red feeder shrimp from Ocean Rider (iron horse feed) work great for this. If a fine enough needle is used, they will survive a short while after being injected — long enough for their twitching and leg movements to attract the interest of the seahorse and trigger a feeding response.
Leslie Leddo recently cured a seahorse with tail bubbles using this technique. She found that a 1/2 cc insulin syringe with a 26-gauge needle was ideal for injecting frozen Mysis or live red feeder shrimp. They plump up when injected and ~1/2 cc is about the most of the solution they can hold. There bodies will actually swell slightly as they are slowly injected and excess solution may start to leak out. The 26-gauge needle is fine enough that it does not kill the feeder shrimp outright; they survive long enough for the kicking of their legs and twitching to assure that they will be eaten. So if your Vet or family doctor will prescribe the Diamox for Apollo, who is after all a member of your family, ask them also to provide a 1/2 cc insulin syringe with a 26-gauge needle.
If you are using 250-mg tablets, Leslie found that 1/8 of a tablet provides enough Diamox for several days’ worth of injections. In other words, 1/8 of a 250-mg Diamox tablet provides enough of the medication to inject two shrimp daily for about 5 days. So each day, I would take 1/8 of a tablet and shave off approximately 20%-25% of it to make the Diamox solution for that day’s injections. (NOTE: if you are using 125-mg Diamox tablets, adjust your dosage accordingly — that is, start with 1/4 of a tablet and then shave off 20%-25% of it to make the Diamox solution.) Then crush the Diamox you have shaved off and to a very fine powder and dissolve it in a small quantity of water. Use the result solution to inject two of the live feeder shrimp and feed them to the affected seahorse immediately after injecting them.
Each day you will have to prepare fresh Diamox solution to inject the shrimp for that day’s treatment, so just repeat the steps above each day. Your seahorse’s gas bubble should show improvement rapidly, with 2-3 days. If not, after you have fed him injected shrimp for 3 straight days, give him a break from the Diamox for a few days and try again. (Diamox can suppress the appepitite, so feed him unmedicated/uninjected shrimp for a few days to keep him eating and help restore his appetite.) Then feed him Diamox-injected shrimp again at the rate of 2 per day for a total of 3 more days, but this time increase the dosage of Diamox slightly (shave off a bit more of the tablet each day when you mix the new Diamox solution).
Best of luck with your your ailing Sunburst! I’m happy to hear that your Pinto is still going strong.