Kalkwasser... not a complicated word or process at all. In fact, the word itself is the only imposing thing about it (and that’s only because it’s of German origin--we can forgive that). In America we have heightened the understanding of kalkwasser. At The Fish Store we have perfected and simplified its use. Kalkwasser’s primary purpose serves to increase calcium ion concentrations in seawater. Secondarily, it can increase pH--but not via the same chemistry as a buffering solution or a calcium reactor. Why are calcium levels important? For those of us who maintain reef aquariums, many of the organisms we nurture require calcium to build their “bony” structure (very similar to our bone development)--this includes hard corals, soft corals and some marine alga. Other elements are needed for this process as well, but calcium is by far the most abundant in their composition. It is vital these organisms have a sufficient supply of calcium to lay down new “skeletal” structures to grow and thrive. And, unlike vertebrates, these organisms do not have finite lifespans--they never stop growing. Vertebrate bone development slows and eventually stops as we age. Corals and alga, under perfect conditions, never die--hence they always need a steady supply of calcium for constant growth. Their skeletons are the foundation of reef structures. Therefore, we must provide calcium to our captive reef ecosystems if they are to flourish.

Kalkwasser is calcium hydroxide. When mixed in seawater the calcium and hydroxide ions dissociate. We’ve already discussed the importance of the calcium ions. Now, hydroxide ions can greatly increase pH. But their effect on pH is very temporary when compared to buffering compounds that contain carbonates (your system’s buffering potential). Hydroxide ions quickly boost pH, but this boost quickly dissipates if the water has sufficient buffering capacity. BUT, if you maintain your water change regime (5-10% weekly, depending on bioload), the buffering potential of your system should not be a problem AND your pH stability should not be a problem either. This is because all quality salt mixes have excellent buffering capacities and appropriate pHs when initially mixed in RO/DI water. Kalkwasser supplements a stable system pH. However, a supersaturated kalkwasser solution has an extremely high pH. For this reason, it must be administered in very small doses--you do not want to artificially (i.e., with supplements rather than the normal biological gradient that will exist naturally in a well-maintained system) raise the pH of your system more than one-half degree in any 12 hour period (or visa versa). Again, the key to successful maintenance of any system, especially reef systems, is consistent stability. Quick, sharp increases or decreases in pH are not consistent or stable. Some people profess success in their systems despite inconstancies (fluxes in pH, salinity, temperature, and other parameters). To this end, some organisms are more resilient than others--but your goal should be to provide for them all--not just the tough ones. Also, we often don’t know what other factors may be affecting success in such systems--usually it is something even unnoticed by the keeper.

We recommend the use of kalkwasser over any other method to maintain calcium levels. But, as stated previously, it must be administered slowly and cautiously--particularly until you have familiarized yourself with its use and affects on your system. For this reason, its use best suits systems with sumps. Before setting up your kalk-doser, determine how much water your tank evaporates on a daily basis. Then purchase a container that holds at least 3-4 times this amount of liquid (Kent Marine’s AquaDose units are perfect for this, minus the IV drip). This container will hold your kalkwater and you’ll only have to refill it every 3-4 days (note, the size of your container dictates the number of days you’ll go between refills). Plumb the supply line from your container into your sump wall with a float valve. Now, as water evaporates from your system, it will automatically be replenished with the kalkwater. We do have one recommendation that varies slightly from common kalk-dosing methods. Your mixture of kalkwater should be 1-2 teaspoons kalkwasser per gallon RO/DI water. Also, in your kalkwater container, place a powerhead (Aquarium System’s Maxi-Jets are excellent compact units for this purpose). You will need to make the opening larger if you use the Kent AquaDose units in order for the powerhead to fit. Put the powerhead on a ordinary timer and set it to come on 4-6 times per day for 10-30 minutes per time. This will depend on the smallest time increment you can select on the timer, but that is inconsequential. It could even stay on all the time--but that would wear down the powerhead a lot faster. The object is to keep the solution constantly stirred up. Also, keep any significant openings on the kalkwater container loosely closed. You cannot seal it completely, especially because you’ll have the powerhead cord coming out, but try to limit the access to air as much as possible (with a loose lid or cellophane wrap). Precipitates will form when the carbon dioxide in air reacts with the kalk solution--this is inevitable and will require periodic container cleaning (say once every 6 months). So try to limit the kalk solution’s exposure to air. Remember, however, that you cannot make the container completely airtight or the solution can’t gravity feed to the sump--incoming air must replace outgoing liquid. We have found this method to work extremely well and its a lot less messy than other methods that have been popular over the years. The results are amazing and once you’ve gotten the hang of replenishing the kalkwater--it’ll be a snap!