Seahorses require dedication and persistance.
Their tank should be species only. More aggressive eating fish will out compete their slow, deliberate feeding habits.
They requre low water flow, as high flow rates will stress them into not eating, they will simply grab hold something and stay there until the high rate is gone, or they die. You can force move them, but they will just find another tight hold.
Seahorses require feedings in which the food is exposed to them for about 20 minutes at a time. This allows them to consume slowly. Before you decide on seahorses...ensure you have a small like 5.5 gallon tank to keep live brine if need be. Be prepared before hand.
Air in the tank is dangerous to younger and older seahorses...often times the bubbles are mistaken for food and consumed. The consumed air, unless ejected, will creat bouyancy problems, and can (and often does) lead to infection and then death. They can also (so I have been told, never witnessed this before) absorb bubbles through their skin causing the same problems.
If at all possible, purchase captive raised. Not only to preserve natures livestock...but to ease in your feeding routines. But back to the being prepared. A seahorse can change its appetite from frozen to live in the drop of a dime...
Seahorses when one is properly aware of their unique habitat and feeding requirements, are a very interesting, as well as entertaining species to keep.
You can keep a cleanup crew with them as well. Dwarfs and snails would be the limit, maybe a peppermint shrimp or two as well.
I have kept a yellow tail damsel in with my horses without incident. He ate his food and the horses ate theirs.
Read, read and read somemore.