Co2

not an expert but i guess size and cost. You can have reduction is space. You have to consider also max temp to make CO2 work at its best and cycles/years to make the best use out of it. Electricity cost may be a plus also. Look into side effects of CO2 if ur grow is in your apartment.
 

c526

Member of the Month: Jan 2015 - Plant of the Month: Jan 2015
I use c02 in my sealed room,i dont use it in my tents,its a waste of time

I have a c02 meter,I tried to fill the tent with c02 and watch the meter,as fast as I was pumping it in,it was pumping out and filling the basement
In a tent fresh air is just as beneficial,imo
 

Sphnx

Nug of the Month: Oct 2014 - Plant of the Month: Nov 214
I agree with C but it does help to introduce Co2 into a tent a couple times a day. There is no reason for you to install a Co2 generator in a tent its way overkill. If anything buy a exhale bag. Those work really well in tents.
 
i use sugar, yeast and water in a soda bottle with a pipe to my fan so that the fan blows it on the top of the plants i think it works you change it every two weeks i have four bottles right now (4 kg of sugar in 4 packages of yeast in 4 two litre bottles on two fans one on the tops and one from down up)