If you are looking for CO2 for your grow room then the best solution is to go to your local welding gas supply store and rent a CO2 bottle. It is cheap for the gas and you only pay a monthly rental fee for using the cylinder. You will need to buy your own CO2 regulator in order to control the flow into your grow setup. The welding store will sell these too.
Products like CO2 Tabs are not effective because they produce very little gas, which is simply lost due to the constant extraction of air from your growing area.
A CO2 cylinder will literally have 500 times more CO2 in it compared to tabs.