I say keep the CO2. It definitely cant hurt.
Light energy is what is going to help you achieve the results you are looking for as long as you have the genetics. Some buds just don't dense up like others. Indicas are what you should focus on or a hybrid.
I hate to tell people to go out and buy new stuff unless that is what they are asking. Since everyone has suggested new lights, I want to jump on that band wagon. LED lights will produce much better results and a whole lot less heat issues.
Sorry about the purple, I took the pics with my phone. These 4 plants are in 7 gallon pots inside an area that is 3.5' x 4.5', With the LED's I use, I can enlarge the space to 6'x6' if needed.
Front left plant is a rare Indica phenotype of the Jack Herer strain. It will produce dense hard buds, but the one in the back to the right is a Sativa dominant (Golden Goat) and it produces fluffier buds. Although the LED still tightens them up good. In the other pictures you can see the dense growth and fat stalks these lights produces.
LED's produce 90% light and 10% heat. Those HID lights are just the opposite. 90% Heat and 10% light. Plus only a small % of the HID is usable to the plant. Unlike the LED which is spectrum tailored so the plants uses most of the light produced. Very efficient plus LED lights last on average for 5 years, so no bulb changes and one of these lights I use produces 400 true watts of completely usable light for only $500-$600.
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