corals can sting seahorses, plus when the seahorse grabs onto the coral it will bother it and make it close(may even kill the coral). most fish can not be housed with seahorses as the fish are aggressive eaters. good type of fish to have with seahorses are pipefish, jawfish, firefish.
Sea Horses are awesome in their own right. If you want to get a really cool fish that goes with them, check out the blue dot jawfish. They are beautiful. They are jumpers though so have a lid. Some people put sea fans and gorgonians with them. You can also get a lot of cool looking macro algae to put in the tank.
Good luck. I have a barnacle blenny, and a black ray goby who lives with a candy pistol shrimp. They are very peaceful fish that are unlikely to compete with the seahorses or bully them. But I have no experience with keeping seahorses. My two A. Ocellaris clownfish rule that out.
If you have a temperate vs. tropical species of seahorse, the catalina goby would be a great companion.
Hi....
Do you know what size tank you are going with?
You can absolutely keep a pair of clownfish with seahorses (I wouldn't go with a pair of maroon clownfish though)......I have been doing it for a long time now. I have a goby in there too..... No issues at all.
I've wanted to setup a tank for seahorse's as well, probably not soon, but when i do i'm leaning on just tying in a big fuge for my 60g cube with nothing but macro algae, and having the seahorses in there opposed to setting up a new tank. Thats a route to consider.