Aqua Man
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I agree and disagree with supplemented co2... you need to run lower humidity and higher temps than what's usually calculated under VPD... co2 slows transpiration rates because the plant photosynthesizes more efficiently and thats how you combat it.This is another old thread but to revive it, unless your running co2, there would be no reason to have humidity levels at 70% to even 75% during flowering. The reason humidity levels are run higher with CO2 is because the temps run higher up to 95 degrees with LED. And to keep your VPD in a good range you have to run RH around 70-75%..
I run LED lights and the leaf surface temps runs .5 - 1.8 degrees Fahrenheit COOLER then ambient air temperature due to all the air movement needed to move the CO2 around the room and also to keep pests and mold in check. Because my leaf surface runs cooler then ambient air I run my flower rooms at 90-95 degrees with RH at 65-72% as my AC kicks on and cools it down to 90, my RH also decreases to about 65% when the AC kicks off and as the heat builds back up the RH also does with all the biomass... When the lights go out the room cools to 75 and my RH slides down to 55% with lights out. After week 6 co2 is down to 800ppm for week 7 and 600ppm for weeks 8 and 9. When I ramp down co2, I also lower temps..the last 3 weeks it’s 78 degrees lights on and 65 degrees lights off..the humidity only goes down as low as 50% I also run a hybrid setup that exhausts room air every 6 hours.
to grow with with both LED and CO2 really requires you to run hotter which in turn requires more humidity, to do it you need a sealed room and very good air movement both below canopy and above and all around. It’s high maintenance teetering on the razors edge. This type of operation isn’t your typical tent grow you have to have the equipment in place to DOMINATE your growing environment and have backup ventilation system in case something goes array.
Now there is a whole can of worms that plays into this and no one size fits all.