In the USA, whats a good way of buying co2? How do you apply it to your grow?

[GeddaLiddleHI]

if you want a real easy, and practically free way to get CO2 to your plants, check out the CO2 dispensing bottle i rigged up for my grow here. i reccommend usign the Mk. II version that implements absorbant fabric in the hole since it's more consistent, but that's just my recommendation...