CO2 only serves plants, not fish. The reason you want to have your CO2 levels at optimal levels within the first hour or two is because once lights turn on, plants will start consuming CO2 fast. In fact the first hours of photosynthesis are the ones where the plant consumes the most CO2 if I am not mistaken. If your CO2 is not optimal at that moment you will see a big dip in CO2 concentration in your water colum which will then take time to recover. You don't want that.So is it better for the plants and livestock to get to the desired CO2 PPM as quickly as possible or does it save on gas?
Read this < Surface agitation & gaseous exchange in CO2 injected tanks >, you will thank me later. 🙏