Typically you want to get your calcium levels to 425/475 before attempting dosing kalkwasser. Kalkwasser in and of itself is not very good at raising calc levels bur more as a way to maintain it after you get it where you need it to be.
When kalkwasser is dosed or dripped into the tank, the following procedure is more or less used. One to three teaspoons of kalkwasser are added to a gallon of water that is to be used for makeup water. The kalkwasser is then gently mixed to saturate the water with the kalkwasser. I say gently, because an important consideration in using kalkwasser is to minimize the amount of air that enters the water during mixing.
When kalkwasser is combined with highly aerated water, it forms calcium carbonate, which is not useful in the aquarium. After the gentle mixing, the kalkwasser mix should then sit for a period of a few hours to allow settling of any calcium carbonate that has formed. This, along with some unmixed kalkwasser, will form sediment on the bottom of the container. After settling, the saturated kalkwasser (the liquid above the sediment) is siphoned off to be used for dosing. (More on dosing in a minute.) When using this method of kalkwasser addition, it is important to use the mixed kalkwasser within a few days. Old kalkwasser mix will lose its concentration of calcium in solution, which results in little calcium addition to the aquarium. And it is important to not dose the sediment, which is a mixture of calcium carbonate and calcium hydroxide. Dosing this can result in calcium precipitation, excessive elevation of pH, and decline of alkalinity.
The other method, and generally more preferable method of mixing and dosing kalkwasser, is through the use of a kalkreactor. These devices may go under the name of a calcium reactor, kalkreactor, and Nilsen reactor, to name a few. In fact, there is another type of reactor (to be discussed later) that is also called a calcium reactor that is quite a different device. For the sake of this discussion, I will use the term "kalkreactor". A diagram of this device may be found in Sprung and Delbeek's "The Reef Aquarium, Vol. I", pg. 245. There are also a number of do-it-yourself (DIY) projects on the Internet for building one of these. Essentially, a supply of kalkwasser is inserted into a sealed reactor chamber. Within the chamber is a magnetic stirrer/spinner. Using a dosing pump, water is drawn from a fresh water reservoir and pumped into the reactor chamber, where the magnetic stirrer periodically mixes the water and kalkwasser. The pressure build-up from the dosing pump within the reactor forces the saturated and milky kalkwasser then to be dosed into the aquarium. The advantage of this method is that the calcium concentration of the kalkwasser remains higher, and the mixing procedure requires far less attention.
The procedure for dosing kalkwasser is important. A saturated kalkwasser mix will have a pH that can exceed 12. If added too quickly, the aquarium pH can rise significantly, which stresses the tank inhabitants. Beyond this, a significant pH spike (usually above 8.5 - 8.7) can cause a calcium/carbonate/magnesium precipitation. This leaves the tank with stressed livestock and often less calcium than before dosing. Ideally, a pH monitor and/or controller should be used when dosing kalkwasser to insure that tank pH remains below 8.5, however this is not a requirement. If dosing kalkwasser without a pH monitor, it is important to drip it slowly (around 1 drop/second maximum) into a water stream in a sump or in the tank itself.
The disadvantages of kalkwasser may be fairly apparent. If mixing it for makeup water, it can take time and diligence to mix it properly, and dose it properly. A kalkreactor greatly reduces the inconvenience, and can provide a highly saturated kalkwasser mix. Another disadvantage is that kalkwasser additions are limited to the amount of water that is used to replenish from evaporation. Many complain that they just can't get the calcium levels up using kalkwasser alone. Often it is cited that kalkwasser is a highly effective method for maintaining calcium levels that have been obtained by the use of other methods, particularly by those who mix their own kalkwasser. Those utilizing kalkreactors report that they are able to build calcium levels, as well as maintain them in a relatively trouble-free way.
The advantages of using kalkwasser are many. First, kalkwasser, when mixed properly, is highly saturated in calcium, and leaves no other residues in the aquarium. This accomplishes the primary goal of kalkwasser use, namely increasing calcium availability to aquarium inhabitants. Kalkwasser helps to maintain alkalinity in the aquarium. On this point, I want to highlight that kalkwasser does not increase alkalinity, but rather helps maintain alkalinity by neutralizing acids that would usually be neutralized by resident buffering agents. The result is that carbonates in the aquarium, and thus alkalinity, is preserved. Kalkwasser helps maintain pH. This occurs not only due to the preservation of alkalinity, but also because of the high pH of kalkwasser. When properly dosed, kalkwasser can be used as a tool to gently increase pH to more desirable levels in the aquarium. This is useful in combating the natural trend in closed systems of pH decline. Finally, kalkwasser is known to precipitate phosphates out of solution. What this means is that when calcium hydroxide enters the water, it causes phosphates to fall out of solution. This is helpful in preventing/removing problem causing algae and cynobacteria blooms.
