First Timer, JOTI God Bud.

Noticed a bit of sudden yellowing, I am assuming it is nitrogen. But I only have Gaia Green 3-0-3, 4-4-4, and the 2-8-4 power bloom. The issue is most likely my Ph pen being out of range, I am going to have to calibrate it weekly. I just top dressed with the 2-8-4 about a week ago, so I am a bit unsure, I don't wanna add too much more and possibly cause other issues. Watering about a litre per day now, watering every 2 days it seems to dry out too much.