Plants need C02 in the process of photosynthesis (please say I got that right). They take in the C02 and breath in O2 (Oxygen). This is the opposite of us humans. Normal house plants have all the C02 they need already in the air. But in a tank, there is little C02. C02 is not easy. It requiers time and a pH and KH test kit to watch the levels. The main reactor (pop bottle, etc) should be outside the tank. The de fuser is what sits in your tank. This is what will mix the water and C02. ( I think I got those mixed up) For more read the C02 sticky in the plants section.
