What is this yellow stuff around my zoas? I think it's sponge. Why is it forming there? And what can I do to prevent it from spreading or stop it from growing anywhere else?
It's a sponge. I suspect a small H2O2 injection would knock it back without causing excessive harm to the zoas. I had one of those for a while, but it doesn't cause me any issues with excessive growth so I don't worry about mine.
If you can pull the rock out of the tank just pull it out. Then take a toothbrush to it. Most sponges die while out of the tank. Maybe try and chip the zoas off and chip the rest of the sponge off. I have the same type sponge growing in the middle of a sps colony I can't get to it without tearing the colony apart.
I can't get to it without tearing the colony apart.