I assume there is some sort of adjustment on the skimmer, I would raise the "bubble height" further up the neck of the skimmer.
You could also try giving everything a thorough vinigar cleaning, especially any injectors or venturis.
But with such a low bioload and depending on what else you do for maintenance and water quality, you might not have a ton to skim. In which case I would increase the bubble height even more, and skim really wet.
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