Good stuff. Especially regarding the detail on the effect of ph imbalance on the leaf. Source? Thats the kind of info i like to know about.
Should also add (was quite baked the night i was answering this, completely misunderstood the question at first) The reason i connect the blackened leaf edges presenting so fast as a PH issue over actual nutrient deficiency, is because calcium is an immobile nutrient, and how calcium deficiency presents with lockout vs real deficiency can be a dangerous place to be in DWC. A PH swing down in DWC, It's usually caused by overfeeding, but the plant will begin to display signs of calcium and magnesium deficiency, prompting you to add even more if not experienced, further amplifying the problem. Being able to identify the difference between the two is absolutely mission critical when growing sativas in DWC.
The only way an immobile nutrient deficiency can even present so quickly is if it in fact a total lockout through PH which effects even the immobile nutrients already in place being used within the plant.
Examining what PH lockout is at the biochemical level and in simple terms: Actual deficiency will present and build over time with an immobile nutrient. However a sudden PH swing can even prevent the plant from processing and using the nutrients it has already taken up. Some nutrients stored, should the acidic swing be rapid or deep enough, can actually change their molecular state from an acetate, to a hydrochloric salt within the plant. Often this changes the fundamental properties of the compound in question. When calcium and magnesium, already processed and stored, immobile nutrients (i actually dont remember if magnesium is mobile or immobile), changes from an acetate to a hydrochloric salt within the plant, the effect is the same as the calcium suddenly vanishing. And it being an immobile nutrient, once the damage is done, the damage is done.
Just in case someone reading doesnt know what immobile or mobile means: Some compounds, like all plant usable forms of nitrogen, are considered mobile, the plant can move it around. It can choose to let lower leaves die and move them to a new position within the plant. Plants can recover physically from amending a mobile nutrient deficiency. Immobile nutrients like calcium, once in place,, cannot be altered or repurposed directly by the plant. This is why immobile nutrient damage is not repairable, you can only improve the vitality of the new growth that isnt fully developed yet.
Those dark leaf edges are actually late stage calcium/magnesium deficiency signs. If this happened in a single nutrient cycle, it's only possible that it was a PH issue.
Overfeeding in DWC tends to present as burnt tips, not margins, and plants tend to become very dark green with a leathery and textured appearance to the leaves and the vascular ridges. Often becoming glossy as well.
I would be willing to bet money, the OP's PH just drifted too low too fast because the plant was pulling water faster then it was grabbing the solids dissolved in it, creating run-away acidification, locking out immobile nutrients and triggering, in very short order, what looks like a host of deficiencies.
