It all comes down to the PPFD level you're aiming for...
If you're goin with over 1000 PPFD them its a good idea to introduce co2. On the other hand, if you're not over a 1000 you can run your grow without it. And dont get me wrong, a 1000PPFD is about 43.20 DLI for a 12/12 light cycle, which...