Nothing is official at IC Rag. It's just another forum with a lot of newbie bullshit, witness your link.....and this recommendation - "The plants can be foliar feed at ½ teaspoon/quart of Epsom salts" Ridiculous. That will not only induce a toxic issue but severe leaf burn.
This guy's take on N toxicity looks more like the subject plant lost its root system to rot. The best take on elements, toxicity and deficiency, is in Mel Frank's book.
Since the subject of water quality has come up, see if you guys could work with my well water! (next page after this page)
https://www.rollitup.org/marijuana-plant-problems/251235-stop-blaming-issues-ph-people-8.html