The seahorse is an enchanting fish, and his strange little body means he has special requirements in a home aquarium. His gills aren't as efficient as those of other bony fish, limiting his gas exchange. With no stomach, food whizzes right through his digestive tract. Take these considerations into account, and mimic his natural habitat to give your seahorse the best of care.
Room to Move
Unlike other fish, the seahorse is vertically oriented; he'll use as much vertical space as you can give him. The minimum tank size for seahorse is 18 inches tall, but since these fish can be up to 8 inches long, look for a tank height that's between 2.5 and 3 times the uncurled length of your fish. For larger seahorses, such as Hippocampus ingens, that means your tank must have a minimum of 65 gallons for a pair of seahorses and an another 30 gallons per additional pair. Many species require a minimum tank size of 29 gallons, with an additional 15 gallons per extra pair of fish. Smaller species such as H. fuscus require a 20-gallon tank and an extra 10 gallons per pair. The smallest of all seahorses, H. zosterae, should live in a 5-gallon tank; add 1.5 gallons per each additional pair of fish.
Water Temperature and Chemistry
Just as tank size varies according to the species of seahorse you bring home, so does the temperature and salinity. Tropical seahorses require water temperatures between 71 and 74 degrees Fahrenheit. Subtropical seahorses need cooler water, running between 67 and 70 degrees. Temperate seahorses live in water of 64 to 66 degrees. Seahorses naturally live in saltwater, so a freshwater aquarium won't do for them. Your pet store can provide the appropriate seawater mixes for your aquarium -- don't use kitchen salt -- and you must keep its specific gravity between 1.020 to 1.024. Similarly, the water's pH should mimic the ocean's, meaning your aquarium should strive for a pH reading between 8.0 and 8.3.
Clean, Breathable Water
To re-create the seahorse's shallow natural environment, your home habitat needs to have gentle currents that turn over the tank volume three to five times an hour. The seahorse's biology presents some challenges in filtering and cleaning, as he quickly passes whatever he eats through his digestive tract. A hang-on-back filter will keep the water moving, and a protein skimmer will keep nitrates and excess organics in check. The skimmer will provide aeration, helping your seahorse breathe easier with his less efficient gills.
Food and Company
Depending on your seahorse's appetite, feed him once or twice a day; give him thawed, rinsed frozen food such as mysis shrimp, krill, plankton and ghost shrimp. Some species are too small to eat anything but frozen brine shrimp, which should be enriched since brine shrimp don't contain sufficient nutrients. Offer supplements such as fish vitamins and live food weekly. Hand-feed your seahorse a few morsels at a time until he won't eat any more, or use a feeding station. Competition for food with other species in the tank can cause a problem, so choose your seahorses' company carefully. Fan worms can add some visual interest to your tank without threatening your seahorses. Snails are welcome. If you must have other fish, make sure they won't threaten your seahorse -- no court jester gobies or barnacle blennies. Spruce the tank with safe corals such as daisy or clove polyps. Sea stalks serve as hitching posts where seahorses wrap their tails to rest.