Yes, sir, I’m quite sure your male has white tail disease, commonly known as tail rot. Yes, your five-gallon nursery tank should make an admirable hospital tank!
The bacteria that cause infections such as white tail disease or tail rot are highly contagious, and often a species of Vibrio, so I would not place the female in your hospital tank with the male. If possible, it would be a good idea to place the hospital tank immediately adjacent to your main tank so the male and his mate can see each other through the glass. That would be a good compromise that would allow the pair to remain in visual contact without risking spreading the infection.
White tail disease/tail rot is a deadly affliction if untreated, so don’t concern yourself about the brood of babies your pregnant male is carrying — if he dies, all of his unborn young die with him.
However, I can tell you that even newborn seahorse fry can typically tolerate the same chemotherapeutics and treatments as adult seahorses, so I wouldn’t anticipate any adverse effects from treating your male with antibiotics. Beta-glucan It is not a drug but rather a natural substance derived from Baker’s yeast. As such, it is completely non-toxic and will not be harmful to the fetal fry.
You can never say for certain that antibiotic therapy won’t have any affect on the embryonic young, but if your male’s pregnancy does not go well it is far more likely to be due to his health problems and the stress associated with them than to any of the treatment options we have been discussing.
So get him in treatment as soon as possible, Nigel! Here’s hoping he responds well and delivers a healthy brood of fry.