I’m very sorry to hear about the accident your seahorse experienced. The intakes for filters and powerheads in a seahorse tank need to be shielded or screened off to prevent a curious seahorse from being drawn up against the intake by the strong inrush of water. When these unfortunate incidents happen, it is usually the tail or the snout of the seahorse that is injured.
In your case, the whitening of the snout indicates that the blood circulation to that area has been impaired. No doubt the seahorse was stressed out and traumatized by this experience, so it’s not surprising that he is not doing well right now.
The greatest danger right now is that a secondary bacterial or fungal infection will take hold in the affected area of the snout, and I would suggest isolating the seahorse in your hospital tank so that it can be treated with a regimen of broad-spectrum antibiotics to protect it against this risk. If the barrel of the snout becomes swollen and tender, the seahorse will be unable to eat properly and starvation and malnourishment can complicate the situation.
Furan2 would be a good medication to use for this problem, Mitchell. Furan2 is a good combo medication that consist of two nitrofuran antibiotics (nitrofurazone and furazolidone) plus good old methylene blue. That gives it both bacteriostatic and bactericidal properties as well as anti-fungal properties, and makes it effective against various gram-negative and gram-positive bacteria. But the medication will have a negative impact on your biological filtration, so Furan2 should be used only in a hospital tank.
A bare-bottomed aquarium with plenty of hitching posts will suffice for a hospital ward or Quarantine Tank (QT). Ideally, the hospital tank should have one or more foam filters for biofiltration along with a small external filter, which can easily be removed from the tank during treatment but which can hold activated carbon or polyfilter pads when it’s time to pull the meds out. It’s important for the hospital ward to include enough hitching posts so that the seahorse won’t feel vulnerable or exposed during treatment. Aquarium safe, inert plastic plants or homemade hitching posts fashioned from polypropylene rope or twine that has been unraveled and anchored at one end are excellent for a hospital tank. No aquarium reflector is necessary. Ambient room light will suffice. (Bright lights can breakdown and inactivate certain medications and seahorses are more comfortable and feel more secure under relatively dim lighting.)
So just a bare tank with hitching posts is all you need for your hospital ward. No heater. No reflector. No lights. No substrate. You can even do without the sponge filters or external filter in your case, just adding a couple of airstones to provide surface agitation and oxygenation. That’s it.
In a pinch, a clean 5-gallon plastic bucket (new and unused, NOT an old scrub bucket!) can serve as a makeshift hospital tank. It should be aerated and equipped with hitching posts and perhaps a heater, but nothing else. This makes a useful substitute when the Quarantine Tank is occupied or in use and a seahorse needs treatment.
Stay on top of water quality in the hospital tank/bucket with water changes as often as needed during treatment, and and when you are treating the occupants for a health problem, re-dose with the medication(s) according to directions after each water change.
In short, I would recommend treating the injured seahorse with a regimen of Furan2 in your hospital tank as soon as possible. I would also suggest obtaining some live adult brine shrimp to help keep the seahorse eating while it recovers. A portion of the live adult Artemia can be added to the hospital tank where it will survive until eaten, and the softbodied shrimp may be easier for the seahorse to slurp up through its tender snout. Surrounding the seahorse with tempting softbodied shrimp will hopefully encourage it to eat despite the injury to its snout.
Here’s hoping your seahorse can make a complete recovery from its unfortunate accident, Mitchell.