Yes Xcrispi that is a rule of thumb that many do use, but I haven't found a real documented grow that compares using nutes on a typical schedule compared to using the nutes at the same level as the CO2 PPM.
Razz CO2 controllers run between 5 and 900 bucks for a decent set up. Mind you, this doesn't include the CO2 tank or propane if you go with a CO2 burner rather than a CO2 tank. With a good CO2 control package you will be able to make sure your CO2 is staying at the programmed levels because there will be a probe that monitors the levels in the room making sure that they are not to high or to low. You will usually have a photo sensory monitor that makes sure that once lights go out that the CO2 is no longer released. You will probably have a timer that can allow you to program desired CO2 treatment times, and all of the connections, solenoid, tubes and so on as well.
Adieu