My LFS has a BIG sign on the seahorse tank and at the cashier station warning against how difficult it is to keep seahorses (which I think is nice and very responsible of them). They can be very hard to feed as they do not regularly accept prepared foods and they are not aggressive eaters. If you are not a SUPER advanced saltwater keeper, I don't think it would be a good idea. Even the smallest most minor thing can result in the death of a seahorse - they are extremely sensitive. Seahorses need to be introduced into VERY mature established tanks - and if i am not mistaken, isn't yours fairly new?
Also Seahorses are not strong swimmers and have no defense against aggression.
All in all, I would say No, please don't get a seahorse.