Leaf tip curling sideways, canoeing – reoccuring problem

[Withzerai]

Hi growers,
I need your help with my plants.

I’ve been dealing with this issue for a while now. Sometimes it’s worse, sometimes not as bad, but it’s always there – new growth comes in twisted, the tips fold up like a taco, and the leaf edges curl upward.

On my last run it got so bad I scrapped all the plants, thinking it was a russet mite infestation. I replaced everything I could: new watering hoses, pots, carbon filters, HEPA filters. I bleached the room, heated it to 40 °C (104 F) for two days, then bleached again.

This time I switched from soil to coco so I could be 100% sure what I’m feeding, hoping the problem would disappear. Unfortunately, it’s back again.

Setup:
Sealed grow room with a 2.4 × 2.4 m tent inside. The room works like a lung room with AC and dehumidifiers.
Added purge fans that exchange the air every hour for 15 min.
Inside the tent: scrubber, humidifier, and bottled CO₂.
Four MarsHydro TS3000s – one for each 1.2 × 1.2 quadrant.
Medium & pots:
Clones started in 0.5 L plastic pots.
Transplanted to 11 L fabric pots sitting on pot risers.
70% coco / 30% perlite mix.
After transplant they looked rough (pale green with purple stems) for about a week. Once roots poked out the bottom of the pot (1 week after transplant) they perked up. Currently at the end of week 4 veg.
Watering:
Running RO (my well water is trash at 0.7 EC, i don’t even drink that sh*t). Starting at 0.0 EC.
Add CalMag up to 0.3 EC, then Canna A+B to 1.3 EC total.
pH down to 5.8.
Watering twice daily (0.5 L at lights on, 0.5 L mid-day).
Solution temp ~23 °C.
Runoff is heavy, around 0.8 EC and ~6.5 pH.
Coco never dries out, I keep it saturated. Algae growing on the perlite top layer.
Environment:
CO₂ ~800 ppm
Temps: 27–28 °C day / 23–24 °C night
RH: 68% day / 60% night
Leaf temp usually 2.5–3 °C below air temp
VPD ~1.1 kPa
Lights at 45% intensity, 0.9 m above canopy
The tent extractor ramps up with temp/humidity, minimum speed is set to 40%. Two oscillating fans blow across the lights (not directly at the plants).
I’ve checked for pests for hours with 50× and 1000× scopes – nothing. I add BTI to feeding solution occasionally to prevent fungus gnats.
The canoeing happens even on lower growth, so I thought it wasn’t light stress. But I’ve noticed about an hour before lights out the leaves fold even more. I’ve since dropped intensity to 30% with the lights at the same height.

The previous run that i’ve ditched was in soil with Biotabs fertilizers, I’ve managed to find a photo – as you can see the sideways hooking of the leaves is exavtly the same as i have now.

All input is appreciated, thank you.

[Author]

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