As far as i know seahorses are for expert level hobbyists and are kept in a tanks exclusively designed for them.
In most cases, they only eat live food such as copepods or amphipods.
You can populate you tank with live copepods/amphipods. You can buy them on ebay.
This is a good time to order them because the temperatures are low and there is less of a chance that they will survive standard shipping.
You should be able to find some good deals... 2,000 live pods for $29 and 5,000 for $39.
Acclimate them to your tank temperature and specific gravity. They are usually raised in 1.027.
Once you put them in your tank, leave the light off for a few days and let them settle. I hope this helps.
Good Luck.