Another very important aspect is the pH level . Keep a close eye on the pH during the first hours of a CO2 injection, or until it is leveled. Macronutrients are usually in ample supply in the aquarium water, micronutrients have to be added from time to time, and are best placed into the substrate. Nitrates should be kept at low levels, as excess nutrients will promote algae growth . You should add macronutrients only if you have undetectable levels over an extended period of time.
Most plants can store nutrients for later use.
Other things you should know Airstones and pumps will lower CO2 levels through a chemical reaction. Plants should provide enough oxygen for your aquarium, eliminating the need for an additional source of oxygen such as an airstone. Surface turbidity will also deplete CO2, which means not every filter type is best suited for a planted tank. Undergravel filters are not recommended either, because of the difficulty to clean and more importantly because UGF's will oxygenize the substrate. This will make some nutrients unavailable for the plants, since they can take up nutrients more easily under oxygen free conditions.