Butterflies!! Who's got em.... in a Reef.

[Myka]

Ya, I think 40g is too small for any Butterfly. What about a nice Fairy Wrasse?

Also, keeping zoas with SPS isn't the best idea as the zoas release toxins that irritate SPS. Zoas have a tendency to take over like a weed too, and will sting and damage SPS. If you do try it, you will have to run a significant amount of carbon to absorb the toxins from the zoas, and large amounts of carbon are also known to reduce polyp extension on SPS. It's kind of a lose, lose situation.