I know that I'm not going to shake the world with this, but...
Did you ever stop to realize that while you stand hypnotized by your plants, you could be wasting valuable, bud-nourishing carbon dioxide? If you direct your breath in a controlled manner on your plants in a still room (fans off) for 15 minutes, then allow them some time to digest it, you can give a large dose of CO2 without tanks or burners. If you can do it a couple times a day, you've got a carbon dioxide enrichment program implemented. Congrats!!
Now I won't spend a fantastic amount of time on figures, and I won't bother listing sources... you can do your own searches and calculations if you don't like mine.
I found that we exhale around 1 kg of CO2 a day.
44 grams (g) of CO2 is 22.4 litres (standardized)
1000g / 44g = 22.7
22.7 x 22.4L = 508L/day
43200 exhales/day x 1.2 litres (avg. exhale vol.) = 51840L, 508 of which are CO2
508 / 57840 = 0.0097 or
970 ppm of CO2.
I've also heard a general 3-5% of every waking exhalation is CO2, which would be
3000-5000 PPM of CO2.
No matter which way you slice it, we've got a resource here that it would be silly not to use, if at all possible. I know some of us can't make the time to get out to wherever we grow every day, but I also know that a lot of us spend a ridiculous amount of time getting our noses burnt by HID's. I used to practice deep breathing exercises with my face almost buried in the canopy...
Talk about a relaxing place to medicate... err, meditate

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E4A2S