Week 4 DWC update, running into some clawing

Running a 4-bucket DWC setup in a 4x4, currently day 28 from flip. Strain is Gorilla Glue Auto, been in the tent since late October. Lights are a 600w HPS paired with a 200w actual draw LED bar for side fill. Temps sitting at 76F canopy, 68F res, RH around 52%. VPD is roughly 1.2 kPa which should be solid for mid-veg transitioning to early flower. Nutrient schedule has me at 850 ppm (500 scale) going into week 4, EC around 1.7. pH locked between 5.8 and 6.0, checking twice daily. Res changes every 7 days, topping off with pH'd water at 5.9 in between. That part has been dialed in for a few runs now, no issues there. The problem showed up 4 days ago. Tips on 3 of the 4 plants started clawing downward pretty hard, classic nitrogen toxicity look. I dropped the ppm from 950 down to 850 and it slowed the progression but hasn't reversed yet. Leaf color is still very dark green across the board. I've been second-guessing whether it's actually N-tox or if high temps in the res could be causing some root stress that mimics the same symptom. Res temp did spike to 72F for about 18 hours last week when my chiller hiccuped. Could that brief spike cause clawing that lingers 4 days later even after the res came back down? If anyone has run into this and identified the actual cause, i'd appreciate the input. Dropping ppm further to 750 feels risky this close to heavy flower development but i'm open to it if that's the consensus.

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Experienced1d ago

Late to this one but i want to push back a little on the "just drop ppm" advice because i think you might be chasing two problems at once and treating them like one. That 72F res spike is not a minor thing. Roots can take on a kind of invisible stress from warm water that shows up in the leaves days later, even after temps normalize. The clawing you're seeing could be the plant struggling to uptake properly because the root zone got cooked a bit, not because you're actually overfeeding. If you drop ppm hard right now based on a false N-tox read, you might starve her going into peak flower. What i'd do is get a good look at your roots. Pull a bucket lid if you can. If they're still white and healthy looking, lean toward the N-tox theory and yeah, back off the feed. If they're showing any tan or slime or funk, that's your culprit and ppm is kind of irrelevant until you fix the root zone first. Hydro guard or a diluted h2o2 flush would be my next move in that case. The dark green leaf color though, that part does still point toward nitrogen being on the high side regardless. GG phenos can run sensitive. I've noticed heavier feeding lines tend to push clawing earlier with glue strains than with something like a more sativa-leaning cut. 850 at day 28 from flip feels a touch aggressive to me personally but it's not outrageous. Don't go below 750 yet. Diagnose the roots first.