Lois,
If you call Dan today, will you mention to him that I was considering a ciliate cause. I'll send him a PM to explain my thought process to him. More or less, the seahorse did not respond to Furan-2 or Neomycin+TriSulfa. It also did not respond to lowering the tank temperature to 68*. To me, that screams that its not Vibrio, so I'm not very hopeful on the Baytril. That leaves a few common treatable bacterial infections, some of which could be affected by Baytril (we have seen salmonella in seahorses before, for example); and a few common bacterial infections that are not treatable (Nocardia, Mycobacteria). It also leaves non-bacterial infections. Considering the unknown raising conditions, these are more possible than usual. Granted, some cannot be treated, and some require very specific and difficult to aquire medications (like chloroquine). But, on the other hand, some don't. We can't use FW and formalin because of the open wound, but we could at least do a last ditch effort at trying praziquantel. I don't know of any negative interactions between Baytril and praziquantel, so I would go ahead and do that and cover both of your bases. Your best bet is to feed the praziquantel to the seahorse inside gutloaded adult brine shrimp (2tsp prazi in 1 gallon of water, mix thoroughly, and leave adult brine shrimp in the water for 2 hours before feeding them to the seahorse). If you can't do that, a bath treatment would be better than nothing (follow dosage on packaging). If you can't get prazi, let me know what dewormers/antiparastics you can get, and we'll go from there.
The Baytril is Enrofloxacin, and I thought that was something that had already been sent to you...??? It is far, far, far better for it to be injected, and considering how bad off he is, that is the only way that I would go. However, it can be tube fed to the seahorse, I just am not 100% on exactly how effective the med is in that form b/c I'm not 100% on the degree of chelating that happens. For injection, the best place is in the belly. There is something about the muscle in the tail being to dense or not getting enough blood flow... anyway, the instructions that Marty (Labdoc) gave in the injection thread are accurate. If you can, write them down or print them out and bring them to your vet and your vet may be able to show/explain.
Baytril should be dosed at 0.01mg Baytril per gram of body weight every other day for 5 treatments. It is best to weigh your seahorse. If you are unable to, it is reasonable to assume a body weight of 10 grams and use 0.1mg of Baytril every other day for 5 treatments.
P.S. Yes, do a complete water change before using the Baytril.