It's possible that with the addition of CO2, the plants are consuming
nutrients much faster than before and therefore a deficiency has been
created in one or more elements. Have you checked your nutrient
levels? What about substrate fertilization? It's possible that your
substrate has also been stripped of nutrients due to the increase in
plant uptake. I'm sure there are other possibilities, but this is the
first one that comes to mind.

What does your fertilization routine look like?

Hope that helps
Giancarlo Podio