Sponges can have some crazy toxins in them, so it's not surprising that nearby zoas might be effected.
I didn't really realize that until you said this Joshua! I've never done a lot of extensive research on sponges, as we've never "intentionally" bought any, but it IS pretty amazing what kind of toxins they can have...even toxins that will cause rashes (and the like) on people's hands that touch them. I guess I've been pretty lucky up to now, as I have touched a few sponges by mistake - I've GOT to be more careful!

OH - BTW - I've got something else growing on another zoa rock...it's kind of soft, and a dark purple-ish black color. The zoas that are on the rock don't seem to be affected, but they are not spreading any either. Looks like some type of encrusting coral, but it *could* be another type of sponge (I guess?). Has anyone had anything that looks like that in their tank?

Thanks Joshua for your input. I will do it immediately
So how are the zoas doing? Were you able to pry that sponge off the rock?

W.