Hi
The ammount of Co2 required will vary from tank to tank and has many variables such as Tank Size, what plants you have, your lighting, If you are using aditional fertalisers, your surface movement at the top of the tank etc etc
Because of this the only accurate way to measure whether you have enough Co2 would be to use a drop checker with 4dkh solution. This way, when the drop checker is green you know that your running 30ppm of Co2 (Which is the recomended ammount however you can push to more, but you have to watch your fish carefully)
Regards,
Craig