a fairly large system, 30+ gallons so everyone has their own territory. Anything thats slow, keeps to themselves and is peaceful, Cleaner shrimps are good, any snails are good too, with crabs i recommend getting them small like crabs that won't grow more than an inch so they don't attack the seahorses. stay away from any sea cucumbers, you can get starfish just make sure your tank size is compatible with their needs. also rule of thumb most invertebrates like to be in an extablished aquarium where they will most thrive off of the nutritents.Happy Reefing.
