Just for starters, you may want to keep an eye out for a possible tank cycle; it doesn't seem as you have cycled your tank.
Depending on how much light you have, you may not even require the CO2. While it is not essential under low light conditions, there is no harm in having it. How much light do you have?
In terms of CO2, in my opinion, the best way is to use a CO2 drop checker, and not a pH monitor. The CO2 drop checker will help determine whether you have ~30 ppm of CO2 in your water column (the optimal concentration). Once this concentration is reached, you can set your pH monitor to keep the pH at the noted value.
Depending on how much light you have, you may not even require the CO2. While it is not essential under low light conditions, there is no harm in having it. How much light do you have?
In terms of CO2, in my opinion, the best way is to use a CO2 drop checker, and not a pH monitor. The CO2 drop checker will help determine whether you have ~30 ppm of CO2 in your water column (the optimal concentration). Once this concentration is reached, you can set your pH monitor to keep the pH at the noted value.