Gosh how I hate disputing the merits of co2 enrichment.
Well now honestly, some of this comes from memory, but as I recall, pot has been around a very long time on this earth, and many hundreds of years ago, the co2 levels were much higher here. Over time for whatever reason (global warming, i dunno why) this changed. Point being is that pot does not like the present count of co2 in the air, it is use to higher amounts. Pot plants can pretty much utilize a very high concentration of co2, so long as it also receives a higher amount of light and nutrients to help boost the speed at which it wants to grow at.
The following is an exert from greenmanspage, a notible grow guide that suggests use of co2 will double yr yeild, while I hold that claim to be, if you know exactly what you are doing and everything is perfect.
CO2
Elevating carbon dioxide levels can increase growth speed a great deal, perhaps even double it. It seems that the plant evolved in primordial times when natural CO2 levels were many times what they are today. The plant uses CO2 for photosynthesis to create sugars it uses to build plant tissues. Elevating the CO2 level will increase the plants ability to manufacture these sugars and plant growth rate is enhanced considerably. CO2 can be a pain to manufacture safely, cheaply, and/or conveniently, and is expensive to set up if you use a CO2 tank system. CO2 is most usable for flowering, as this is when the plant is most dense and has the hardest time circulating air around its leaves. If your strictly growing vegetatively indoors, (transferring your plants outdoors to flower), then CO2 will not be a major concern unless you have a sealed greenhouse, closet or bedroom, and wish to increase yield and decrease flowering time.
Even though CO2 enrichment can mean 30-100% yield increases, the hassle, expense, space, danger, and time involved can make constant or near constant venting a desirable alternative to enrichment. As long as the plant has the opportunity to take in new CO2 at all times, from air that is over 200 ppm CO2, the plants will have the required nutrients for photosynthesis. Most closets will need new CO2 coming in every two or three hours, minimum. Most citys' will have high concentrations of CO2 in the air, and some growers find CO2 injection unnecessary in these circumstances. Some growers have reported to High Times that high CO2 levels in the grow room near harvest time lower potency. It may be a good idea to turn off CO2 2 weeks before harvesting.
What I find humorous is that you had no problem accepting the 600% increase this cd claims to add, but you debate the merits of co2 and a measley (by comparison) 10 to 40% increase
lets put the big guns away, okay