Let me get this straight, You folks are growing in Soil and using Chemical Nutes? Thats not how you get the most out of your bud. I've grown my cut of OG with Synthetics and with Organic Compost tea. Ill tell you any day that my yield was better, smell was greater and I was able to back a lot more food into my teas that would have burnt the plant if you did the equivalent in Synthetics.
Also If you dont want to spray bloom boosters on, then you probably dont want to feed the same thing to your plant but through the roots...
As per the Co2 Question, You want to have really good ventilation and you should be good. Look up some DIY Co2 guides and maybe do that the last month of flower when the plants are using the most.
Chobble