Are you keeping them in a reef tank with other fish? That's going to be hard. Seahorses are very slow eaters and will not get enough food if they are in a tank with other fish. Plus, you shouldn't really keep stinging corals in with them, as they will get stung so soft corals would be best.
Another thing is that they like low flow, which also limits your coral availability. They need a lower temperature than most reef tanks, about 74 - 76 depending on the species of horse you want to get.
From what your signature says, I think that you'd have way too much flow, you would have to find a way to disperce it through the tank, or modify the flow.
I hope that you'll get captive breed horses, as they are easier to care for and well, aren't ripped from the ocean. Please do a lot of research before purchasing these animals, they are amazing but require a lot of work.
Check out seahorse.org while you're at it.