CO2 in a tent is absolute bollocks, if you want to utilise CO2 then you need a sealed room as plants don't need oxygen to grow. There's no need for air exchange, only extraction of heat from the lamps (cool tubes and ducting!)
The CO2 bucket thing and yeast/sugar is also bollocks.
Carbon Dioxide levels should be high, particularly during the FLOWERING PHASE . Growth rates can be increased dramatically if the CO2 level is near 700 ppm. 300 ppm (Outside Air) 700 ppm (Ideal) 2000 ppm (Plants Burn) 5000 ppm (Death)
They charge £200 for a CO2 sniffer for a reason, there's no way you can get anywhere near 700ppm from a CO2 bucket and it's laughable to think you could get it from yeast/sugar!
Most guys who run a sealed room shoot for around 1200-1500ppm CO2.
It's pointless messing with CO2 unless you've got your growing skills dialed in 100% and you can't get any more from the strain your working with under normal conditions.