I know there are sponges that grow in zoas and cause issues,
but it seems like a colony grew on a spongy material and now it's poking through.
Like the sponge was under the frag and now it's growing through it.


Any ideas?

I've read that three times and still have no idea what it is that you're talking about...

eh?

That's exactly the word I was looking for

??

I think the same thing happend to some of my zoa's. Ended up having to frag the colony into 2 pieces. kept the spongless half and tossed the other (the zoa's were completly smothered). Damn sponges

Some zoanthids live symbiotically with sponges, though those types sometimes appear to be less hardy.
http://www.wetwebmedia.com/zoanthid.htm

that sounds cool. make sure to frag it underwater if you go that route.