Can you give your plants to much Co2.
Yes! You can suffocate and burn your plants by having to high a PPM in your growbox.
Like any nutrient or mineral; 1500 ppm is the Max ppm you would want to subject any plant to.
Make sure you have adequate ventilation switched on by a C02 meter. i.e. When ppm’s reach 1500, or less, your ventilation should turn on and clear the room, box, etc…Milwaukee instruments sells a meter with a piggyback switch that does this.
Hope this helps. You did not say whether you were using a tank, or homemade generator.