Could it be beneficial to add CO2 into the water supply just a theory I had and wondering if anyone else has had the same idea and tested it.

no. Oxygen is needed in the reservoir. though Co2 in the environment if your tempetures are on the high side can be beneficial though I gather you know this. Plants only use photosynthesize when the lights are on so giving them extra co2 in the res might not be a smart idea. Though this is just my opinion. Best of luck for your projects though and for all your plants :) 👊