Need Help recognizing POSSIBLE mold!

So im a first time grower and today i was watering my baby and noticed some white stuff on about 4 leaves. This is only happening on the very bottom of her. Please give me good news. Mold? Calcium build up? Will it destroy the plant? we are about one and a half weeks into flowering in so cal.

im not so sure that was great advice lol...

Spray them, tops and bottom of leaves now with diluted neem oil. Takes about 24hrs to be affective; repeat every five days for at least two applications.