I have a seahorse tank and I have a royal gramma and a black and white clown in with the horses. However, they are in a 55 gallon and the horses don't seem to mind the fish. I also closely monitor feeding times. I feed my horses out of a feeding dish so the fish don't bother their food. IDK about corals, obviously anemones or anything that stings will be off limits. Closely monitor the seahorses once you put anything in with them to make sure they aren't getting stressed out.