Profitting from breeding marine specimens is like creating Pharmaceutical medications.The first pill costs millions of dollars, the second pill on costs "bupkis." lol
Translate that to fish, all of the things bribo12 said is correct plus you have to have all the things in place for WHEN or IF the event happens. You could go for years and not get them to breed or you could have success right away. The next step is that seahorse young are not really agile at finding foods. In a recent documentary I saw about seahorses, it took some of the hatcheries trying to raise the horses multiple tries to get enough food to the ponies in order to get them to survive. You will need to experience all that in order to know what you need. That can get expensive.
So all in all, you need to be prepared to spend a lot of money until you get the system down.
Hope this helps