Shagrathanswered grow question 5 years ago HI!
I'm in the same boat as you are rn! I have been talking to china and you can buy CO2 sensor/controller (TUNGDY is the company) and it costs like ~200$ and it connects to solenoid valve thats connected to CO2 gas bottle. With that controller you can adjust youir desired CO2 PPM level in the growing area and its all automated. Cheapest option is to buy big CO2 bottle (I have 10kg) and flow meter and control the level by hand.