I never really measure run-off. It could mean alot of things. mainly, by the time the water gets to the bottom a good amount of the nutes get trapped/absobed into roots/medium so that can change it alot. I usually ph around 6.5-7 for all of growth. Which isnt too hard because my tap comes out at the lower side of 8 almost 7.9.
so after nutes im sittin at around 6-6.5 so a couple drops of ph up and im good. Dont even gotta ph it the second time.
but yes, that looks like a mag def and the curl could be from lock out like you said.
temp messes with ph as well. Colder, the lower, warmer, the higher. I think. Either way make sure youre not drawing cold water straight form the tap or somewhere cold or warm, then ph ing. Try to get it to room temp around 72 i think is best for ph testing. I remember seeing all this stuff about temps on teh back of a calibration solution bottle. How at different temps its more or less basic/acidic.