Okay, if you are limited to a 10-gallon aquarium, realistically the only seahorses you can consider are the miniature species, and dwarf seahorses (Hippocampus zostrae) are certainly your best bet in that regard. Any of the larger seahorse species would be unable to breed in a small aquarium of 10 gallons and would-be susceptible to depth-related problems such as gas bubble syndrome in such a shallow tank.
Dwarf seahorses are great for beginners and ideal for breeders. Pint-sized and prolific, these pigmy ponies are the perfect pick for anyone primarily interested in rearing or for any seahorse keepers who can’t afford to devote too much money or space to their hobby. Hippocampus zosterae is the best choice for the novice who wants to learn more about keeping and breeding seahorses before moving on to the big boys. More budding seahorse keepers have cut their teeth on dwarves than all the other seahorses put together. H. zosterae is the right pick for newbies who would like to try their hand with seahorses for a modest investment, or for hobbyists with a tight budget, or aquarists looking for captive-bred seahorses that are a snap to breed and relatively easy to raise, or anyone captivated by keeping tiny elfin creatures no bigger than your thumbnail.
The good news is that your 10-gallon tank is large enough to safely accommodate a whole herd of the dwarf seahorses, including dozens of the adults and all of their offspring. The bad news is that you cannot keep any anemones in an aquarium with the seahorses. Anemones are stinging animals and they would injure or kill any of the dwarf seahorses that came in contact with them, which is inevitable in a small aquarium of 10 gallons. Likewise, it is not advisable to keep any live corals in a dwarf seahorse tank, since hydroids will eventually be introduced into the aquarium along with the live coral, and the stinging hydroids will also wreak havoc on the pigmy ponies and their babies. So you can keep a whole colony of dwarf seahorses in your 10-gallon aquarium, Jenny, but you will have to do without the anemones and the live coral for the sake of the ponies.
Since you are new to seahorse keeping as well as the marine aquarium hobby, Jenny, the first thing you need to do is to learn everything you can about the care and keeping of seahorses and the basics of marine aquarium keeping. You will have to do your homework and read up on the subject before you attempt to keep any seahorses and I would be happy to recommend some good books for you. For example, an excellent place to start would be to read the book "The New Marine Aquarium" by Michael Paletta. Next I would suggest you follow that up by perusing "The Conscientious Marine Aquarist: A Commonsense Handbook for Successful Saltwater Hobbyists" by Bob Fenner. Those are both outstanding books for a beginner that will give you a good grasp of the basic things you need to know to maintain a marine aquarium.
After you’ve had a chance to digest The New Marine Aquarium and The Conscientious Marine Aquarist, and have a better understanding of the basic principles involved in keeping a saltwater aquarium, you should next study a good guide book devoted for seahorses. Alisa Wagner Abbott’s outstanding new book on dwarf seahorses (The Complete Guide to Dwarf Seahorses in the Aquarium, 2003, 144 pages) would be perfect for you, Jenny. You can order all of these books online from Jim Forshey at the Aquatic Bookshop (<http://www.seahorses.com/index.shtm>) or from Amazon.com and the other major booksellers, or you can find them at your local library. (And Alisa’s dwarf seahorse book is available from Ocean Rider on this website.)
Next, contact me off list ([email protected]) and I will send you tons of good information on the care and keeping of dwarf seahorses, including how to set up your 10-gallon tank to create an ideal environment for these pint-size pigmy ponies. (You’ll probably want to stick with some simple, foolproof air-operated sponge filters or undergravel filters for such a setup.) And I will include detailed step-by-step instructions for cycling a new aquarium to establish the biological filtration and get it ready for the seahorses.
Best of luck with your first venture into aquarium keeping, Jenny!