My clean up crew consists of 12 blue legged hermits and 6 scarlet hermits. They pay NO attention to the seahorses. I'd NOT get any other crabs, arrow, mythrax etc. as they may ACCIDENTALLY nip at the tails of a seahorse.
I also have a 3 inch red/pink banded serpent star (I'd stay clear of the "brittle" kind, as they've been known to hunt-especially the green ones)
I also have 12 nassarius snails, 2 mexican turbos and 8 astrea turbos.
I put in two pepermint shrimp to eat any aptasia.
Finally, I've put in about 6 live ghost/grass/glass shrimp who also clean up any scraps of mysid that float to the back of the tank, out of the reach of the ponies. As a bonus, they carry eggs and have babies about every two weeks. The seahorses snick up the babies whenever they can.
The orange sponge would be perfect in the pony tank. They don't sting like corals and would act as another hitching post. Also, pony tanks, being slow water tanks, and typically higher in nutrient load than a reef, would benefit from the additional filtering of ANY sponges.
Zoas and shrooms are okay in a pony tank. Yes, they could trap babies if you are breeding, but, keep in mind....
Baby seahorses, after leaving the pouch, float to the water surface. They do so in order to feed on plankton and to gulp air and fill their swim bladders. If they do not float, they will have bouyancy problems for their entire life. With that said, they will probably NOT get mixed up with zoas. You'd have to remove them from the tank into a rearing tank anyways. In a rearing tank, I'd not have any zoas.
The feeding dish is a nice idea, but my ponies have no use for it. They do NOT want to find food in a dish. They would rather hunt the food so I drop in the mysid and let it free float. Others who have ponies say that theirs DO eat from dishes. Mine do not. I've since removed the shell.
I got a 4th pony this weekend. Another female. I now have 1 male, three females, and two ORA Orange Male Reidi on order from a local supplier.
Dave