I know a lot of people will say that pods dont eat zoa unless they are dying... but I had a colony slowly recede from the same exact reason. Whether it was from the pods stressing them out and keeping them closed or if they were melting away themselves, it was definitely the problem.
From the research I did, I found that pods dont typically attach zoa, but once the pod population gets too big and without a natural predator, they start to run out of food and begin to eat coral.
What I did was get a wrasse (or you can get any pod eating fish) and within 2-3 days, once the pod population was almost gone, the zoa literally came back like nothing happened!!!
Best $12 investment I ever made. Saved me from losing $50 polyps from completely disappearing