HELP !!!!

[pecan2phat]

I would say literally impossible, they have tentacle like growth so injection would be futile.
Zoas are very hardy and can stay out of water for a long time. You can try the tweezer route and get as much off as you can. Mine came in on a Zoa colony as well!
I would also say that zoas are tough enough even to be tooth brushed under running tap water for a short amount of time. But I would do this only if the Zoas are healthy and strongly matted in attachment or you risk tooth brushing the polyps off.

 

[BloopFish]

Consider a silicate removing product for your tank. Sponges require silica to grow, so once you manually remove the sponge and also remove the silicates - they won't be able to grow at all. It is like if you removed all the calcium, there would be no way for corals to grow in that case. Be careful if you have sps though, a lot of silicate removing products also remove phosphates and sometimes nitrates as well and a swing in these parameters may stress them out.

 

[piranhapat]

I heard salifert eXit flatworms kills them.