nanafish, I want to clarify something. I can't be 100% sure since I'm trying to "diagnose" from home photos, but I think that the seahorse has a small prolapse of the pouch lining. However, the prolapse of the lining won't cause floating, it is just a secondary problem that develops out of the problem causing the floating (likely pouch emphysema).
Can you clarify whether what is protruding from the pouch appears to be tissue, a clear "bubble", or fluid/pus?
Have you attempted another pouch evacuation? If the gas trapped in the pouch is not in the pouch lining, an evacuation can release it so he's not floating anymore. This is a relatively simple procedure, but when not done, it can cost the life of the seahorse.
Have you used the Diamox at all (either as a bath or a pouch flush)? The Diamox should help, at least temporarily, with the buoyancy issues, but it will affect appetite, so if he's already not eating, be prepared to provide live foods to tempt him; and be prepared to tube feed if that doesn't work... Remember, seahorses can only go roughly 4 days without food.
Not trying to pressure you to update the thread, but treating seahorses is pretty time sensitive, and if there is an infection in the pouch (or elsewhere) in addition to the gas in the pouch, there is limited time to take care of it. If you don't already have antibiotics on hand, I would get some. I would also bring the tank temperature down to 68* to help prevent infection (by no more than 4 degrees per day).
Speaking of, what are your water parameters? Specifically, ammonia, nitrate, pH, and temperature? Is the pH stable? Any changes in the tank? Any big algae blooms? New additions?
