IME seahorses require low flow or flow broken up into several returns so there is no strong current in one area.
They need lower temperatures to help prevent bacterial infections.
Seahorses need several places to hitch (wrap there tail around) in the tank. I like to use
tonga branch rock because it can double as a hitch and LR. I'm not a fan of fake things in my system.
The smallest tank I would go with would be a 29g tall for any of the commonly available seahorses. This would include species like reidi (common names brazillian or Long snout), erectus (lined seahorse), comes(tigertail), barbouri (striped snout), kuda (yellow seahorse look just like reidi with a variation on the cornet, kuda is actually a species complex with many sub species kuda and kelloggi being the most common in the U.S.) and histix. Some larger species like potbellies, kelloggi, and ingens, need larger tanks. Dwarf seahorses can be kept in smaller systems but need very special setup concerns as well as daily hatching of bbs.
Many corals canbe kept with seahorses, but you must avoid ones that have stinging cells. Even aiptasia can kill a seahorse.
Taller tanks are better to leave them the needed vertical swim room and so show to lessen the chances of Gas Bubble Disease.
IMO I would not keep them with pipefish, which are also syngnathids because different syngnathids have a high potential to be asypmtomatic carriers for different strains of vibrio. In an aquarium the mixing of these strains is highly volatile and causes many deaths. I recommend only one species of syngnathid per system.
I would not buy a tank raised seahorse, but instead buy a seahorse that is aquacultured. Tank raised seahorses are often raised as fry in net pens n the ocean. When the seahorse gets to an acceptable size it is put in a tank and trained on frozen foods. Since the fry are raised in the ocean they have the same exposure to disease and parasites that a WC seahorse would. I would look at seahorsesource.com, dracomarine.com, or Oceanrider.com. IME they are the only places in the U.S. that are commercial aquaculture seahorse facilities. Even some companies like ORA, and Dr Fosters and Smith (who buy from ORA) sell tank raised seahorses that were raised in the ocean. Many of these seahorses come from Sri Lanka. IMHO it is far better to buy from one of the true aquaculture facilities then to buy a Tank Raised seahorse. If you insist on a tank raised speciment I would treat with a fresh water dip on arrival (temp and PH match the fresh water), then a full course of prazipro followed by fenbendaole. A 6 week QT would be the minimium IMO.
If a tank is setup with seahorses in mind they are fairly easy to keep. Most keepers do not go through the time to understand the temperature issues, or the flow issues which is why I believe amny sites state a seahorse lifespan is 1-3 years. If the tank is setup roperly many keepers have gone 5 plus years. JME.
Vince aka VINNIE 
