Sure Nate
CO2 is a gas and passes right through a RO. When it gets to the other side it gets hydrated and forms carbonic acid as the water is depleted from the RO from buffers ands other ions and causes a shift in pH. This reaction continues and gives H + and HCO3-. The CO2 is now in the form of HCO3- anion or negatively charge ion. It then hits the anion bed, which has OH-, where the HCO3- is exchanged for a OH- ion in the resin, thus depleting the anion bed.
CO2 + H2O ------>H2CO3 ------> H+ + HCO3-
The anion bed was...
OH- OH- OH- OH- OH-
OH- OH- OH- OH- OH-
and now starts to become
HCO3-- OH- OH- HCO3- OH-
HCO3- OH- OH- HCO3- HCO3-
until it is full of HCO3-
To calculate the effects of CO2 on DI depletion, divide the CO2 RO water concentration in ppm by the sum of the CO2 in ppm plus the RO TDS in ppm. For example, if you have 5 ppm TDS RO output and 3 ppm CO2 in your RO output water, you are wasting 3/8 or 37.5 % of your anion DI capacity on CO2 removal alone. CO2 can be calculated by just know the dKH of the RO and its pH.
CO2 (in PPM) = 3 x KH x ^10(7-pH)
where KH is dKH in degrees.
A hand calculator requires no math for this.
Chuck's Planted Aquarium CO2 Calculator with Tables
http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm
(NOTE do not try to use this equation or calculator to try and figure out the CO2 in your SW tank, as it is a different equation for it and the same for the calcualor, as the calcualor is a function of the equation given above )
Example, pH 7.1 and 1 dKH = ~ 3 ppm CO2