I would monitor, if by no other method than pH. I would be more concerned with it causing acidification of the water column than causing harm to the fish, and how that acidification might affect what's happening in the root zone. Since CO2 acidification during winter is such a problem for reefkeepers, I've learned it can be an issue in certain scenarios.
I can't recall, but I think my Tetra Laborette kit allows for calculating CO2 saturation by making some calculations based off the pH and alkalinity tests (I'm thinking it's the dKH carbonate test). I'll have to pull out the test kit and see, but I do like colorimetric tests, because I love messing with tiny vials and drops and shit. :D No, seriously, it's a lot more fun than looking at a digital display!