Thanks for great diary, @Roux!
@Baudelaire is right about the lamps. CFL sucks for flowering as you can check in my old topic.
Good choice with bubblers and GH line. It works great in combination and keeping 1/3 dosage is recommended (I see you are measuring PPM 
and that is even better way) .
I’d say that slight changes in pH can be attributed to clay pebbles. I do have experience only with liquid pH adjusters though so I’m not sure about pH stability with powder version… Anyway there are fluctuations all the time that depends on residual salts, type of nutrients and type of pH adjuster. You just want those to keep in reasonable range.