Supplemental CO2 only helps when light, temperature, and nutrition are already dialed in, because it raises the ceiling on photosynthesis a well-lit canopy can reach. In a sealed, high-light room it can lift yields; in a leaky or light-limited space it is wasted money.

Treat CO2 as the last optimization, not a fix for weak fundamentals. Measure, seal the room, and confirm the rest of the environment is ready before investing.