Calathea spider mites

The patterned top of a calathea can hide fine pale stippling. Turn over several leaves and examine the midrib and the place where the blade meets its stalk with a magnifier.

Find mites, then treat the whole plant

Tiny crawling specks with stippling or fine webbing support a mite diagnosis. Separate the plant and rinse both leaf surfaces, shielding the pot from becoming waterlogged.

Follow the spider mite treatment guide for repeated treatment and inspection. Inspect neighboring plants and treat those with mites too. Added humidity alone will not clear an infestation.