Upward leaf curl

I’ve got an issue with upward lead curl and despite reading the sticky threads I am no wiser as to what it could be...

pH drifts from 5.2 to 6.2
Canna nutes at 1.0EC
Fed 15 minutes every 3 hours
Humidity is 40%
Ambient temp between 20 and 22 degrees c
Radiant temp between 24 and 26 degreees c
Clay pebbles medium
400w lamp at 20” from tops

You can see that they look a picture of healthy overall...



This is the issue...




I’ve already raised the lamp considerably in order to discount heat stress. Strain is Critical + 2.0. They’re about three weeks since being popped now...

Help would be appreciated

Cheers

K

5.2 is too low. leaf curl like this is usually due to high room temp. low pH and high temp are two different issues.

Up your humidity 60-65% 40% to low and try 5.5-6.2ph