They are best kept in species only tanks. There are 2 problems with other tankmates. One is agression. The other is competition. Seahorses move rather slowly so they are easy prey for anything agressive. They are also slow eaters so if there is food competition around they will slowly starve. I have 2 shrimp, 1 clown goby and a pearly jawfish with mine. The clown gobies and jawfish are 2 that are supposed to be passive enough to keep with ponies. I still have to watch it with the feeding though. I put a few mysis in at a time and make sure both ponies are eating at every feeding. Right now I am feeding 3 times a day. Once they get bigger I will probably cut back to the twice a day I was doing with my larger kudas. I'm a bit paranoid right now since my new ponies are so small.
I also have a higher bioload than normal because my tank shares water with my reef. I would never have the 2 ponies, 2 fish and 2 shrimp in a 24 if it was a stand alone. I just don't think I could keep the paramaters stable enough with that kind of load on such a small tank. It is recommended that you have at least a 30g tank for them so I am definitely pushing it.
Hands down the hardest thing for me with the ponies is the temp. They like much cooler water than you normally find in a reef. I see recommended temps from 72 - 76. When I was running at 79 everyone at seahorse.org said that was the cause of my problems. I now have a chiller so hopefully these little girls will fare better. One of the problems I have heard with the higher temp is that it is a breeding ground for bacteria. I will never know what happened to my first 2 ponies, but the third definitely died of some kind of infection he was not able to fight off.
