Co2 DEFINATELY increases yield.. what most people fail to realize is that your plants can also take up WAY more nutrients in a High Co2 environment. Your potency will decrease if you use Co2 with the same feeding schedule because your plants dont have the nutrients they need in order to produce more resin! I recommend a "Ramp up" method that steadily increases the amount of food week over week.. while matching the Co2 ppm level with the ppm level in your food. I start with 4 ml/gal of grow, 8ml/gal of micro, and 6 ml/gal of bloom in the first week of flower.. Then week over week I increase the feed by 1 grow, 2 micro, and 3 bloom.. so by week seven I am feeding 10 ml/gal grow, 20 ml/gal micro, and 30 ml/gal of bloom. You MUST also use a B-1 vitamin like "B52" or "Vitamax" as these boost your plants metabolism and will help them handle that much food! If you dont use B-1.. your plants will likely BURN! By week 7 my ppm is around 2200... and I set my Co2 to the same value... Also.. my weeks are only 6 days! feed-feed-water-feed-feed-water is one week... So by the end of week 7.. there are actually 14 days left in the 8 week plant cycle.. during this time.. I turn off the Co2 and flush with solution like Final Phase or what have you... You NEED this much time to flush.. or your plants will taste poopy... haha... Ramping up the feed like this will keep the potency VERY high.. even with use of Co2 :-)