you don't have a co2 dificiency....if you are ventilating your grow space then your not going to be deficient in it. Getting smart with other members who know what they are doing is not a good way to get help around here. Ph is usually 95% of the problem from new posters in here, so when you show up out of nowhere with a question like that, and don't give any details on your grow then you are going to get general answers. Since your asking about a CO2 deficiency it right off the bat tells us you are a rookie, so therefore probably makeing rookie mistakes...like ph issues....Get smart with people here and see how far it gets you.
CO2 deficiency is so rare that none of the 20 some books I have on growing even speak of a co2 deficiency...so good luck trying to find what the symptoms look like. I would guess (since thats all we can do here online, without seeing your plants and being given such vague details of your grow environment) That you are haveing some nutrient problems, which are either caused by over feeding, underfeeding, or yes....ph issues which will lock out nutrients. Good Luck to you. For someone that has been a member here since 2006, I would think you would have a little better grasp on how things work around here.