Watch your PH as the Pro-tect and raise it significantly...
Also, what medium are your growing in?
yeah, i like the protek raising Ph,
after adding nutes which usually drop Ph,
I'm many times on the money instead of 5.6 5.8
Gnome, chances are mate it's a simple case of overfert and backing off on the nutes is what's helped you more than anything.
The leaf curl you showed in that link is typical of low humidity, but the picture above looks like nothing more than a little bit of burn. If you've predicted a bigger draw on nutes because of the increased Co2 and have fed accordingly, and with silica in the mix, I'm 100% sure that's all it is.
That's got nothing directly to do with high VPD, but a knock on effect of it is the higher ec makes the tissue of the foliage more susceptible to burning at higher temps and lower rh.
well at 1st it was over feeding a *bit* too much but not near enough to get nute burn on the leaves.
ive been doing this a while.
the nutes wern't being taken in because the plants were not transpiring. as in--->VPD
so i backed off to water and liquid karma only, it helped a lot but still the prob was there just not that big of an issue
Rh at this time was 55% and only 1 strain thats pictured was the worst,
when i fired up the 6th 1000w lamp 5-7 days later RH dropped to mid 40s, and everything started being affected and the strain pictured started getting solid yellow like kcars pics on post#1
and i was still feeding water and LK, this is the damage your seeing in the pic now.
in the last 3 days Ive raised Rh to bounce between 65% and 75%.
all the probs went away and overnite i a saw a huge difference for the better.
so there is definitely a direct cause and effect between Rh and the probs Ive been having in my case.