This advice, while well and clearly written, is definitely bullshit. I've been growing cannabis hydroponically since the mid-1980's and have found the following to be true in EVERY case. I largely use General Hydroponics Flora series, though I have also used Fox Farm and Advanced Nutrients
Ph Sweetspot
Rockwool media - Ph 5.6 to 5.8
Coir - Ph 5.8 to 6.0
Hydrotron - Ph 5.8 to 6.2
Anything lower than 5.6 results in nutrient lock-out in any medium.
Nutrient Temperature sweetspot has always been 68 degrees F (given a 72 to 78 degree lights-on room temp and a 65 degree lights-off temp)
TDS Sweetspot
This varies according to where in the cycle you are. Suffice to say I follow this regimen:
Clones: 200-400ppm AFTER roots appear (nothing before that)
Veggie: 800 or so, although can go aggressive and boost to 1000 once the plant is well established.
Bloom: 1000 or so for the first couple weeks, then boost up to 1200 for almost any strain. Some strains (old NL#5, etc.) can take up to 1800 if you've got enough light intensity (over 55W per square foot) and CO2 (1100-1500ppm) to ensure the plant can uptake the nutrients.
If I had the space to setup separate systems for research into this issue, I would do so, but on the surface, this is bullshit unless there are other factors involved that would raise the actual nutrient Ph at the rootzone.
OldGrower