Numero uno

as long as your water is clear and relative clean... The ph drops are by far the most reliable and accurate... Iv'e used pens, strips and drops.. And I always go back to the drops. By the large volume test fluid and your golden.

At 12/12 consider yourself in preflower. You'll stay in preflower until after the stretch ends (1-2 weeks). After that I consider it the flower stage. It helps me to break it up this way. During preflower, the plants still want a strong veg nute mix, so it helps me to organize my feeding schedule a bit better by separating out preflower and flower. For the purposes of your journal, I would include preflower as a flower week.

This is a boron deficiency but you need to know why. Check your runoff ph and ec levels and get them both in line. Cheers