This is my first grow and I have a grow box that is 3x4x6ft and am debating if i should add co2. I have 9 plants and 430HPS. Since we're in the middle of winter and it is -30 outside I can't bring in fresh air from outside. Do i need to add CO2 or would it be overkill? I dont mind spending the money to invest in the system if it works but if it doesn't make a difference then i dont want to waste my money. I've done a little pre-shopping research and haves seen that the injection heads are measured in cubic ft./hr. How do i measure this for the size of my growbox?

Thanks for you help!

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try using yeast for the rest the grow to try it out. Probably 2 2liter soda bottles would do it for that closet. Drill 2 holes in the caps big enough for some straws, stick the straws in the tops. fill about half way with suar water 50/50 mix. add a packet of yeast to each of the bottles ( make sure the water is warm to start out ) Give em an hour or so then shake and enjoy. Once activated the yeast will keep on going as long as you dump half out and add fresh sugar water once a week. Move the set up to a new bottle when the others get too nasty ive only baught one packet of yeas going on a year and a half. Plants like it too, seen a definate difference from last grow

here's a link that provides you with how much co2 to emit for your space.

http://www.hydroponics.net/learn/co2_calculator.asp

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I'm thinking of a Master Plan.......

I took that 2 2l bottles and a milk jug..1lb sugar..1teaspoon yeast in each 2l bottle. Run the tubes from the soda bottles with the yeast, sugar,water mix into the milk jug.. Make sure that the tubs from the 2lb go to the bottom of the mj. Then a tube from the mj...above liquid level to plants..I made up a feed tube..it's a quarter inch clear tubing into which I drilled many hole offset from each other. I run that inside my tubs. For 1-2 plants split the feed to each plant. SSplitters can be found with aquarium supplies cheap. That mix should run about a week.

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"between the ditches..below the radar"

yes you do and when you use it you will see i use yeast sugar

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is that tin foil?

Who? What? tf where?

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"between the ditches..below the radar"

You don't need it, but it helps!

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He Who Hesitates is STONED!!!

if i have fresh air from outside is it require additional co2 ?? and if yes should i turn off the intake vents when i add it ? btw alexos i`m in the same situation like you here is winter and the temps are like -20 early morning and like -5 -10 during day but i have freash air coming into my room. my intake fan blows the cold air into air tunel which has wood cube at the end opened from two sides just like this :

outside
intake fan
||
||
||
|------|
blow warm air -> box mix -> fresh warmed air coming
|------|

so the cold air goes into the box and mix with the warm air from a/c or something like that .. and then goes into the room ... with me this work perfect and i can keep my temps to ambient in the room with fresh air even if outside is -25 i home you know what i mean

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I ♥ G R☻W i N G

The air doesn't need to come from outside, just from within the room. if you run the co2 system to each plant, then not as much needs to be produced. planetnatural.com has a kit for $15 and extra tests for $36 for 10.
the trouble with shutting off your vent fan, is heat build up. Best bet is to direct co2 at base of plant, and let venting run.

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"between the ditches..below the radar"