Sorry my friend. I hope that you save something from that colony. A few questions, are any other colonies suffering from the same? Is that your only zoa colony?
Do you have a fuge tied into your system? What about any fish to tame the population of the pods?
Sorry for all the questions, just trying to figure out what else it could be and if you have anything that could be combatting the problem.
This is my theory about pods consuming zoas. I think that when zoas are vulnerable, whether it be from not liking their surroundings and/or having a fungus or the like, that is when I think the pods take over. I'm not completely convinced yet that pods eat the zoas just to eat them. I believe that they (pods) compound the problems already in the tank by smothering the zoa and not letting them recover properly. So a part of the problem, yes - all of the problem, maybe, maybe not.
Good Luck. Keep us up to date.