I still think the pods are not eating healthy zooanthids. If they are taking out the zoanthids, then more than likely the tissue is necrotic. I have seen plenty of pods on my zoanthids, even them eat zoanthid tissue. However, when taking out the colony for a closer look, it turned out the tissue was already damaged.
I'd have to agree with this. To the best of my knowledge they feed off organic detritus & microscopic organisms - phytoplankton & microzooplankton. They will 'bloom' when there is enough of a food source, but usually quickly die off to a lower level and stabilize.
What else would eat these? I'm not sure I'd go with another Mandarin -- when the pod population levels off, you may have an issue with feeding the Mandarin(s).
Hermits eat them, as do most shrimp. Firefish will also eat them, as well as Hawkfish (which may also eat your shrimp).
I think one of the easiest solutions may be to run a hang-on type canister filter. This should filter the bugs out of the water. I wouldn't run it constantly though - you still want a food source for your Madarins.
HTH,