Purple stems and brown spots

Hey friend, So your temps are pretty low...even the day time. Not that the plants can't handle that cause they can, but usually the purple stems i associate with cold temps, phosphorus or genetics. The dark spot...that too could be cold, possibly got wet like mentioned in the previous question, and then chilly temps. Ive had plants slowly turn a dark almost blackish color once the got too much cold weather. Have you tried to wipe away the white part with a moist towel? Also Once the ph is lower watch and see if anything gets better or worse.