Having large spikes with times of low CO2 is probably why it's working ok. But the same or better results could be obtained from running a CO2 controller, enriching to 1200 PPM and letting it drop down to 400 before letting it ramp back up. This makes the plant really use that CO2. There is a technical explanation about plant hormones, stomata and all that jazz that someone posted on the forum if you feel like digging a little, it really helps you understand how the plant uses Co2 and how to get the most out of it.