Fish perceive overcrowding in part, by sensing ammonia in the water. Calcium Discus eggs are 'calcifugous' - the integrity of the egg membrane being dependent on the lack of calcium in their water. Carbon Owing to industrial and agricultural pollution, many aquarists use activated carbon in some form in their water treatment programme. It is only fine for processing water that Discus have not lived in yet. The last water parameter to address is temperature.
Temperature is a trigger mechanism that can be used to induce spawning.
The pair cleans a usually vertical spawning site, perhaps an inverted flower pot. In typical cichlid fashion, the eggs are laid and fertilized. If the parents repeatedly eat their eggs afterwards, they are given until they are eighteen months of age, and then re-mated with other Discus. Alternatively, a 'secret' method may be employed. Discus eggs hatch on the third day after laying.