Well, just go into it knowing that they have a very poor survival record. The experienced and dedicated hobbyists that I know that have tried haven't been able to keep them alive as far as I know, and IIRC, the Waikiki Aquarium has even struggled with them.
Also, I assume you are in Hawaii, since I haven't seen H. fisheri available elsewhere...
Beyond that, even if you are in Hawaii, you are far more likely to be seeing juvenile hybrid seahorses that have been released into a few of the bays and canals in the area; which also happen to have a dismal survival record. Honestly, I'd be trying to get my hands on captive bred seahorses if I were you. Even considering that wild caught seahorses are always more difficult due to disease, parasites, and feeding issues, those available in Hawaii (the fisheri and the hybrids) seem to be even more so.