Lucas,
Brine is not ok for seahorses to live off of unless you are raising dwarf seahorses. If you raise dwarf seahorses, you will need to constantly raise/hatch brine shrimp. If you choose to raise seahorse, it is best to get captive raised ones, and feed them frozen mysis shrimp. If you search the web, there is a site dedicated to raising captive raised seahorses, but we are not allow to post those links here.
Seahorses are not for beginners, but they can be raised with some knowledge, and a good supply of the right kind of food.