I just added some low-light live plants to my tank for the first time today. After I put them in I started wondering if it is necessary to add co2. I added Java Fern, Anubias, and Crypotocoryne. I would like to avoid the added expense of the co2 if it isn't needed. If it matters the plants are all 3-6" tall. Total of seven plants (although some are bundeled and count as one).