Co2,

Hi there! I'm not sure how much you know technology and how much money/time/effort you are willing to put to this stuff. My setup has 10kg CO2 bottle, Co2 monitor/controller and flow meter with solenoid valve for the bottle. I bought the controller and flow meter/solenoid from alibaba straight from the factories. This will be the cheapest option but will take most time and effort 'cos you have to speak directly to the factory etc. This is the company that made my controller and it is by far the cheapest you can find and easy and actually pretty good quality product https://bradecontrols.en.alibaba.com/?spm=a2700.wholesale.cordpanyb.2.63172bc8f9BYNm It might seem overwhelming at first to look at their products but you can ask what you want. I have model: MC6-CH2-W and it has CO2 meter and controller for solenoid valve (You need to buy solenoid separately). The basic principle of this system is pretty simple and automatic. Once you have made the connections between controller and solenoid etc you just simply set LOW limit of CO2 and MAX level of CO2 in the controller. When the CO2 goes below low the controller open the solenoid and the gas flowes to the grow area and when the high is reached the solenoid is closed. So this is cheapest but most effort cos you need to wait and make connections yourself. Something liek this is also prettu simple and chep product: https://www.growbarato.net/en/Co2-enrichment/2165-vdl-co2-dosis-controller.html It has flow meter and timer to adjust the co2 flow and you only need the CO2 bottle for this.