Lois, to be honest, every time that I see you've posted, I would not be surprised to open the thread to find he passed. I tend to be one of those who rarely advises euthanasia. However, if he doesn't respond to the Baytril and the chloroquine, that is where you are headed. My favorite option would be to find an aquatic vet that you can either take him to, or send a biopsy to, so that it can be cultured for things like nocardia and mycobacteria; and, if possible protozoa. That way we would know for sure. Of course, that is difficult and usually expensive. Without knowing for sure, if he doesn't respond to Baytril or chloroquine, on top of not having responded to Furan-2 and Neomycin, it swings us even farther towards the possibility that you're dealing with something that lends itself to euthanasia and sterilization. You have another seahorse, which poses problems with the "euthanize and sterilize" path, so I have my fingers crossed that this is going to work.
And, whatever you do, please, please, please don't expose him to your girl. Time and time again I see someone decide that the seahorse deserves the peace and comfort of its "friends" in its final days, and all that you are really doing is exposing the healthy seahorse to the illness that is killing the sick one.