Cherry blossom,

It could be from keeping the soil wet in which a fungus can form on top of the soil, or maybe the white your seeing is from excess fertilizer, or from using hard-water (minerals)

If you think it's maybe from moist or wet soil, try letting it dry out between watering. I don't water my pothos until it's practically bone dry.
In the meantime if you want, you just scrape all that white stuff out, maybe down and inch or two and add dry soil back and water less.
The right size pot, a good draining mix and better air circulation to help dry soil better will all help.