All my plants were very young when I introduced them ito my tank. (Aponogeton bulbs, Crypts, Vals, Java fern, Wisteria, Watersprite). As they have all but doubled in size, is it common to have to add more CO2 to matain levels? (Seems logical to me) My levels have dropped from 19ppm to 12. Still getting constant bubbles, New 2Litre bottle, same mixture.