Inside of the reactor KWR a rigid circulation pump realizes that the suspension (mixture) of water and calcium hydroxide powder is in abeyance. Above this white lime milk there is the clear lime water solution. The incoming reverse osmosis water (or very soft water) reacts inside of the KWR immediately with calcium hydroxide, that flows into the aquarium.
The aquarium water is enriched with calcium ions. Because of the very high pH value of the lime water (12-13) the pH of the aquarium water is slightly lifted. At the drip-in point of the lime water precipitation occures. The forming hydroxylapatite entrains phosphate. So the phosphate concentration in the aquarium water is reduced (phosphate precipitation).