You are feeding them ghost shrimp right? Why don't you just get a small tank and do a water change so you can use some of the old water to set up a new tank. Take one piece of rock, an air pump, and airstone and you have a hospital tank for a week. Even a rubbermade tub will work. Seahorses won't survive for very long living off whatever is living in the tank unless you constantly feed live brine or ghost shrimp. It takes some time, but you can train them to eat frozen mysid.