I recommend just leaving your Zygo alone. I grow one, and they do that if they're not acclimated to a certain growing location. Particularly if they were grown in a greenhouse, then they get moved outdoors.
It's no biggie. Subsequent growth will produce disease resistant leaves, and eventually the new leaves won't do it anymore. The old leaves will drop, then the spotting will be nothing but a faded memory.
It just looks ugly at first that's all.
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