FYI, gassing at over 1300 ppm is basically useless. Not many can supply the needed light intensity to make that work right, and over 1500 is simply wasting gas/money....
Spurr says it should not be over 1200. He seems to know what he's talking about:
The facts about CO2 ppm: don't use 1,500!
High,
I haven't posted much lately, but I thought this topic was important enough to write a thread. I have written about this topic quite a lot in the past, but I have never made a thread just for this topic.
My goal: to try and kill the myth that 1,500 ppm CO2 is ideal. I want to get it known in the cannabis world, that it's important to not use > ~1,100-1,200 ppm CO2.
In short, the claim that 1,500 ppm CO2 is ideal for cannabis is total hogwash. I challenged anyone a while ago to find a single scientific study showing 1,500 ppm is ideal for C3 flowering plants, or even just to find the reasons why it's claimed 1,500 ppm is ideal in the cannabis world. I assume the myth (yet another!) came from the liked of Ed Rosenthall or George Cervantes or Mel Frank, etc.
If there is interest in the 'whys' I can explain why it's important to not use > 1,200 ppm, ideally we would use ~1,000-1,100 ppm. The effects from "super-optimal" CO2 concentrations range from reduced rate of photosynthesis, to reduced yield, reduced root growth, reduced stomatal openness, increased photorespiration, etc. In other words, nothing good.
The reason why we should ideally use ~1,000 ppm, is for most C3 species (and C4 I think), CO2 "saturation" occurs at ~1,000-1,100 ppm. That means more than ~1,100 ppm (up to 1,200 ppm) isn't going to help the plants, it's only going to waste CO2 and hinder plants if CO2 is about > 1,200 ppm.
The reason why we should ideally use < 1,200 ppm CO2 is the effect high (super-optimal) CO2 has on "Rubisco activase", the substance that turns inactive "Rubisco" into active Rubsico. At CO2 > ~1,200 (and temp > ~89'F) Rubsico activase is inhibited, which in turn inhibits conversion of inactive Rubisco into active Rubisco. And active Rubisco is needed for high rate of photosynthesis, which in turn leads to high growth rates and high yield, etc.
So, to sum up: It's important to keep CO2 below ~1,200, and to be safe and most efficient, keep CO2 at ~1,000 ppm. Night time CO2 should be < ~500 ppm, unless one is trying to reduce dark respiration and stretch, then upwards of 750 ppm can be used for short periods (otherwise leaf chlorosis can set in)
I can fully cite all those claims, if anyone wants to read the academic lit.