Planted Tank Enthusiast
Join Date: May 2015
Location: Phoenix Arizona
Co2 and nutrients (fertilizer) are two different things. I think you need to do some reading on the subject. Simplified its this: plants need light, carbon, and nutrients (macro, nitrate-phosphate-potassium, and micro, iron-and many others). The more light you have the more carbon and fertilizer you need. These all need to be in a balance of the three.
The hard part is finding the balance for your tank. Read the stickies in the lighting section and fertilizers and water parameters section. My preferred fertilizing method is EI (estimated index) which has many different ways to do it based on plant mass in the aquarium, lighting levels and carbon input.