A quick guide on what a hybrid-loop grow system is why, if you live in the same building as your grow space, you might be able to set one up without the need for fresh air OR a co2 generator. This allows you to set up a grow space in some areas that traditionally wouldn't be able to support one, and without the need of a co2 generator makes it very budget friendly.
Co2 Monitor & Controller: https://amzn.to/3cAO7wy
Co2 Monitor: https://amzn.to/2UmMZa6