Hey, I grow in promix and I want my ph around 6.5...When I take fresh soil and add my house water at 7.4 ph to the soil I'll get a run off close to 6.5 - 6.6 I try to ph my feed & water to 6.8 ish ( 6.9,6.7,6.6 ) is good....I dunno man, I usually don't mess with it either... I think they say 5.8 to 6.2 is the optimal range for weed. It could be slightly low, but probably not enough to cause lockout? I don't like the color matching method, everyone has different eyes lol... I'm honestly over this damn auto.... maybe it will be dead by the time I'm done work and I won't need to worry about it anymore lol.
I'm more concerned with low ph than high. My nutrients bring it down on their own and just a drop or 2 of my PH down acid does the rest. I've 2 of the $20 ph pens and I just got 2 rolls of ph tape ( cheap amzon $12) just to double check the calibration is close enough...I don't need 100% accurate I just need to know if I'm too high or too low....and the tape will confirm I'm close with the pens.