most cowfish that I have seen kept successfully were in big 400+ most people put one in a 100 gallon cause the LFS want's to sell it not really caring much about what it's real need's should be. If you kept it by itself in a 100 gallon maybe you could get away with it but why waste the money on something that is like a 35% surviver in captivity. Zebra mantis are awesome and more personable to me a lot hardier too.
mr.reef24