Read a lot before you make a purchase or it may end up being frustrating as this hobby requires patience and knowledge.
here is something from seahorse.org
Feeding
Dwarf seahorses will generally require daily feedings of live food. More often than not this is accomplished with newly hatched baby brine shrimp. The author also recommends feeding 2 day old brine shrimp enriched with various enrichments to keep them at their best health. Nutrition is a big concern with dwarves, and simply feeding them newly hatched BBS daily does not appear to be enough for them. That is why we recommend older enriched brine at least twice daily. Ideally, copepods would be the best food for them but the huge quantity of copepods required is very difficult for the average hobbyist to supply. Consequently, most hobbyists use live brine. Decapsulating and hatching brine shrimp cysts is not a very complicated process. With practice, this becomes a simple daily task. The decapping process is very important, as hydroids are known to survive on the shells of brine eggs and can suddenly appear in your dwarf tank. Hydroids are very dangerous to your dwarves and you will want to take any and all necessary measures to keep them out of your tank. Decapsulating your brine cysts will help to keep hydroids from infesting your system. Dwarf seahorses will appreciate being fed twice each day, three times if your schedule allows it. Feed them enough brine that the tank seems to be experiencing something like a moderate "snow shower". Try to avoid overfeeding. Adjust the amount of baby brine shrimp you put in at each feeding until you find the amount that they will finish in about 4 hours. If there is leftover brine at the next feeding always adjust accordingly.