With your KH, you can reduce PH from 7,6 to 7 (at PH7 you have 32mg/l of CO2)
If you want to reduce PH you need to use Reverse Osmosis water (for reduce KH ... and GH also)
For me it's not necessary to stop CO2 at night, good KH level (from 4 to 6) permit to not have any significant...