Can you post any other shots? A profile of the body would be nice, as well as a close up of the head in both profile and whatever way shows off the cornet the best.
Do you know anything about the horse? I assume that, if the person who sold it doesn't know what species it is, the horse was bought from a retail store. More than likely, this horse should be treated as a wild caught horse.
It could be a reidi (which is what I am going to assume you are referring to when you say "fire red" -- I am not familiar with that being used as a common name for any seahorse species; sounds more like a marketing ploy IMO), but it isn't possible to ID for sure from the photo and information posted.