New sealed room c02 and ac many questions please help

Hi my fellow growers, I have moved from tents and a negative airpressure in a lung room for years back into a dedicated open room again.

I decided its time to try and push things to the next level. I have managed to constantly yeild 300-350g per m2(10.7ft2) dry nugs no bottoms or sugar included. With 3-4 week veg and 7 week flower so really fast turn around. I used a mixture of 720w bar leds and 600w digital hps in coco mix perlite ect. Hand water 1500 ppm low 6s ph. In 3 gal pots a bit less than half gallons waterings

Now i have decided to get rid of my tents and go sealed room for full climate control and add 2 minisplit ac units for redundancy so its 2.5ton together.

Room is 13ftx20 and 7ft 11inch high
I have a massive co2 tank and regulator and controller hooked up.
Im running the room at 84f-88f lights on with 60-70%rh chasing vpd and 78.8f-81f lights off.
I run 3 x 60pint dehumidifiers on different locations 2ft off the ground ontop of a black storage tub. (i know i need Way more then that but funds are limited for now its eating power lol)
C02 running at 1000-1300ppm (i have read so many mixed opinions on what to run) and i have set mine lower today now running 650ppm-1050ppm
Running 1000-1200 ppfd light from mostly 720w bar leds mixed with a 600w hps here and there.

I have did the whole conversion to a sealed environment in week 1-2 of flower that wasn't to ideal. So im new to a sealed room i have many questions.
I have tried to give as much information as possible obviously there is always more i could try and give but i only have so much time. I have 64 3 gals running now with 4 720s and 2 600w hps week 3 of 12/12 for reference.

So my questions are:
1: I have 2x 8inch pipes from the rooms roof that i used to use for a negative pressure so i dumped all the hot air out and let the cold air come im without a fan on the other pipe. Since its probably 7+ foot high on the roof will co2 leak out of it if i leave it open but negative pressure fan off and inlet side open? Since c02 is 50% more heavy then air in theory without a fan pulling air out will i lose major co2? The reason im asking is ive heard its good to vent your air out for 30mins or so on lights off to get rid of unwanted gasses? and for c02 levels to be ambient and not super high during lights off. Opinions? Ive heard many mixed ones... But id love to hear more.

2: C02 levels during veg and pre flower and mid to late flower.

3: feeding ppm in veg, flower ect with Co2. Added Silica? Calmag?

4: i want to run 6-8 720w lights and either do 100 girls in 3gals or cut it down to say 26-36 in 6.75gal buckets? Obviously longer veg what size dehumidifier do I really need some people say you need to size it for the room and others say for the amount of water you give/want to remove from the room. Im considering a 190 pint industrial dehumidifier to replace the 3 mini units but i might need more then just that?

I'll leave it at that for now
Thanks for your time and input it is really appreciated!

Damn, all sorts of people reading but no one replied?

Well, I'm jealous 'cause I'm in a 2' x 4' tent in ambient CO2. I do end up at with good yields (abut 700gm/sqaure meter) but the main reason is that I give my plants a lot of light.

Zero hands on experience with enhanced CO2 but Bugbee recommends 1200 and 1200. I think I've read that CO2 levels don't matter during lights out but I have to wonder about that because stomata are used to take in CO2 but also are used for transpiration.

Different CO2 levels in veg vs flower? Just asked Grok and, yes. More importantly, Grok explain why to change them.

Temps are a big deal with CO2, You can run up to 85° in veg which really boost production. The information in this video is very valuable because most research is done using CO2 so it applies directly to your environment.


The light saturation point for cannabis in ambient CO2 is 800-1000µmol, assuming that light is the limiting factor, and that's strain dependent. Apparently, indicas max out at the 800± mark, while sativas can take advantage of 1k. I routinely grow at 1k in ambient and, seeing that elevated CO2 gives a 30% to 40% increase in yield (depending on whose research you read), I'd look to run at 1200-1500. The rationale for that is simple—crop mass and quality increase directly as light levels increase. Given the opportunity to run CO2, there's no question that my PPFD's would be in the 1500 range, assuming that the plants were thriving at that level, of course.

In that past week or so, I've spent a fair amount of time with chatGPT and Grok. In both cases, I've fed them info about my grow setup and growing processes and have come up with solid recommendations about how to improve my growing processes. After, perhaps, 8 hours of working with them, I will continue to use them.

Re. silica—I always use silicon in my grows. One of the things that Grok recommended was to use it up until the 3rd week in flower because, after that, it might inhibit cell expansion in the buds. Bugbee recommends it (and provides the basis for his recommendation) so I continue to use it. It strengthens cells which acts to strengthen branches and also makes the plant more resistant to disease and infestations.

Re. CalMag - companies sell fertilizers that provide macro and micro nutrients in certain proportions. There is no magic about the ranges of proportions of the chemicals that cannabis uses and, as long as those chemicals are provided in a certain range of concentrations, cannabis will grow well.

Adding a fertilizer, whether it's a "bloom booster" or "CalMag" will tend to change those proportions. Growers seem to see CalMag as a supplement but it's just another bottle of chemicals. If it's not a component of the line of ferts you're using, I wouldn't use it. I have a bottle of CalMag. I bought it when I started growing four years ago and the only use I have a for it is to pour a little bit of it in my RO water so that I can test the pH of the RO.

Re. EC—one suggestion that Grok or chatGPT made was that I increase my EC levels. I've been at 0.8 in seedling and early veg, 1.2/1.4 in veg, and then 1.8 in flower, dropping again in late flower. Both AI bots advised me that higher EC levels would support the higher growth rates that I get from running at 1kµmol. The bot (I don't recall which one) asked me for dimensions of the buds from my last grow along with the weight. the response was that my bud density would increase by increasing EC in flower and by not dropping EC in late flower.