So my humidity has increased by 15% average since going sealed with co2 at 1800ppm. My leaf temps actually running 75 to 76f now vs no co2 at 76-77f. I put in a window unit inorder to cool the room. Im using a 1000w hid and around 12 inches from the canopy. No leaf burns, one plant has a calcium def it seems. . but shared res so im thinking its something else. . but overall. . i had the same issue with the same strain with no co2. Not really posting to fix that issue, more less wondering what vpd charts would suggest my environment would be. Im hydro at 74-75f water temps. I find the warmer the temps, the faster the metabolism. So now does the vpd charting work when comparing slow and fast growing phenos? Wouldnt a faster growing pheno demand more than a slower one. How does vpd take a plants metabolism into effect? Ive never focused on vpd honestly. Can you convince me why I should plz?
I plan on getting a dehumidifier soon. . but do i need one? I run 40-60 rh before co2. Now since im sealed im 50-70 rh. I was going to drop it down to 50rh with controller. . but thats only because i dont want budrot. I guess im not understanding something. .
You're probably not really getting the full advantage of CO2 if you're running such low temps.
If you want to take full advantage of the CO2 you're using, you need to bump leaf temps up to 82-86, and increase humidity to hit your VPD targets. As you get later into flower you can probably ease off the temps and lower humidities. To prepare for this, you should be running IPM the whole time in veg, and making sure you're keeping an extra clean room. Cannabis isn't the only thing that grows well in those conditions (mold does too).
There's an ideal temp for photosynthesis because there are two competing reactions, and you want them to be at their ideal place. With no CO2, you want temps in the mid 70s for that ideal temp. With CO2, it increases the ideal temp for photosynthesis. If you go too warm, photosynthesis actually slows down.
VPD is still relevant, and the same, regardless of whether you're using CO2 or not, it just indicates that you need to further raise humidity at the higher temp (if supplementing with CO2).
VPD doesn't have to do with metabolism, but with the opening of stomata, which in turn controls flow of water and nutrients through the plant, and flow of CO2 into the plant.