The addition of carbon dioxide gas to the grow environment above ambient levels (~400 ppm) to increase the rate of photosynthesis, enabling plants to use more light and nutrients, typically raising CO2 to 1,000–1,500 ppm.
The dedicated CO2 room is a recurring feature of the channel. A key strategic change this run is delaying CO2 introduction until mid-flower (past the stretch), rather than running it from seedling as before. Mr. Q supported this, noting how large nodal spacing became last run with early CO2. Dakota plans to introduce CO2 when plants begin 'thickening up' after the stretch.