Aaroz, I don't know if we are running into a language barrier, but your last post has some correct things and some incorrect things.
First, you have no way of knowing whether or not kalkwasser will be sufficient for any given stony coral system. While it is true that many systems find themselves rapidly outpacing the rate at which kalkwasser can add calcium and alkalinity to their system, (for precisely the reasons you describe), there are examples where this is not the case (see TMZ on this forum, former TOTM winner who for years kept mixed reefs and SPS systems using only kalkwasser, only recently having to supplement with 2-part). It all depends on the individual system.
Secondly, the process you are describing with kalkwasser is true when it is used as a flocculant for water treatment, but the use in reef aquaria is quite different. When you add kalkwasser quickly, the local pH rises and you get precipitation of calcium carbonate which can then adsorb impurities as you describe. However, in reef aquaria we try to add kalkwasser very slowly as to NOT cause such a local pH spike, and AVOID calcium carbonate precipitation. While this surely still happens to some degree, the dominant process is instead the addition of the calcium and hydroxide ions, which can then go through a series of potential reactions (either directly reacting with CO2 or neutralizing free acids or any number of other intermediate steps) to ultimately produce carbonate for use in coral skeletons. In short, the major effect of kalkwasser in reef aquaria is not to help with water purification via the local-precipitation mechanism you describe, but to add calcium and alkalinity.
