Useless. Just spend time with your plants.
What reasoning do you have that it's useless? Co2 can increase the yields massively (i believe 20-40%). Other than the fact it smells like rotten beer it is def a beginning solution to co2. You sound ignorant when you just make comments with obviously have done no research before you commented. I do agree that you dont need to worry abt co2 until you have nearly perfected your setup. Normal air has abt 300 ppm of co2, with another source of supply the plant can absorb abt 1500ppm.
