Cation Exchange Capacity (CEC)
Some gardeners swear by CEC values, while others grow aquatic plants with nothing but blind faith. It is interesting to know the actual parameters of each substrate, but I've seen plants grown in plain sand and gravel. The samples that lacked at least some organic matter or clay, had slightly lower CECs. The big surprises here were Terralit and Tetra Initial Sticks. The zeolite composition of Terralit provides an excellent ion exchanging medium and has good mineral concentrations. The Tetra Sticks, with it's high organic and mineral content, also had a high CEC. The sandy samples had very poor CECs.