if you see one chances are theres more half his size or even 1/4 his size .... they are just white and turn ccolors when they are in zoa gardens . so my guess is you have green zoas in your tank right . and just one will do significant damage
Some feed on sponges, others on hydroids i think, which is the only use for them, if you don't have those, then good bye zoas. Or at least from what I have heard/read
He is a cool looking critter that's for sure. I put it in the sump for now. The white balance on the under water camera is not the greatest. Plus he glowed under the blues