"were you referring to hydro or soil?" I know, stupid question...... but that's the highest number I've heard so far for hydro.

Started wondering about all this 'cause last week, after keeping my pH steady at 5.8 or lower (usually 5.4 - 5.8), I added some microorganisms which for a couple days made it 6.1. I thought I noticed an increase in crystals for the first time, but since it could have been other things I disregarded that observation (could've been the point in the cycle, had just increased res temp to the high 60's, added the bacterias, etc).
That [6.1] pH only lasted 2 days, until a res change. Thinking that 6.1 was way too high, I adjusted again to 5.7 and continued on. The buds don't seem to be getting nearly as crystally as they should, even though plants look really healthy (deep green, no leaf spots/wierdness). Filtered water, 40% humidity, nutrient temps stable 68 - 70 F, quality nutes -- blah blah blah.....
Anyway just as I was about to try high pH again, I saw all these charts (especially the Overgrow one that shows max P uptake at around 5.3).
Since the 2 schools of opinion are really far apart, I guess I could just set it way high (6.3), then after one week set it way low (5.3). And see if there's a noticeable differance. Although with only 4 weeks to flower left, you can't really afford to waste a week.

thanks for all the input