I forgot who asked about this... I'm sure it varies tank to tank, but TMG doesn't contain enough potassium for my tank. My Lamotte kit shows barely detectable quantities using TMG alone. I supplement it with potassium nitrate and shoot for 6 ppm. The easiest thing to do is buy a test kit and see what you need. Jon Wilson http://www.knology.net/~jwilson/plants.htm