Turning to others with more experience is what makes any hobbyist successful. Fortunately for me, I had most of the items I needed to set up the hospital tank quickly, rather than having to go out and buy everything. Of course, Walmart sells small freshwater tanks that have a number of necessary items for cheap. Petsmart and Petco probably have the same. Tank, light, heater, airpump and airstone, thermometer... that's pretty much all you need to quickly set up a temporary tank for sick fish.
Both seahorses seem to look better this evening. I'll try feeding them again in a bit. I found half a ghost shrimp in the tank, so one of the horses definitely got a mouthful.