Even CB seahorses can be succeptible to ectoparasites. When I see scratching activity, my first thought is parasites. First treatment option is FW dip. 2nd is a formalin immersion. Depending upon the setup, either long term bath or 45 minute bath at higher concentration.
To perform a FW dip, get some clean freshwater that is chlorine/chloramine free. Oxygenate it well and make sure the emperature and ph match the tank the horses are in. Place the seahorse(s) in the FW with a hitch post and airline. I usually shoot for 8 minutes. If the horse handles it fine, I assume it has very little parasite load. If it thrashes about and reacts to the FW dip, I assume the osmotic pressure difference is wreaking havoc on the parasites and irritating the seahorse. In those cases, I leave the seahorse in the dip longer up to 12 to 15 minutes.
Can you get a good macro shot of the fins? How about a history and tank setup with description of tankmates? Parameters?
Dan