It's a regulator with PH controller and a bubble counter. It's not showing a reactor or diffuser which is where it mixes the co2 into the water. It's have to have of the two on it.
The Ph controller will turn the CO2 on or off to hit a target PH level.. you usually set it at a fixed value to get around a 30ppm CO2 level in the water. There is a chart you can lookup your current Ph level to determine the proper setting.. PH controllers alone can cost anywhere from $70 to $300+ You'll need to calibrate it as well, usually with a solution of 7.0Ph and 4.0Ph You can get them online.