Dosing Kalkwasser in a Marine Aquarium for Wonderous Results

Those of you that have been in the marine hobby for any length of time are sure to acknowledge just how important calcium can be to the livestock they keep. The big three key components for a marine biotope are calcium, pH and alkalinity with magnesium thrown in for extra measure. Calcium is responsible for enabling corals and invertebrates to grow and produce calcareous skeletons and exoskeletons. Kalkwasser or calcium hydroxide is a great way of introducing, maintaining and elevating calcium levels especially since water changes alone will not suffice in replenishing calcium that has precipitated out of your tank.

Kalkwasser is a German word for lime water. Synonymous with limewater is calcium hydroxide. Calcium is depleted in marine aquariums at varying speeds. Variables such as amount of carbon dioxide in the water and in the ambient environment, livestock population, amount of coralline and Halimeda algae in the aquarium, alkalinity, pH and amount of calcium that precipitates out onto equipment and substrate all have a direct impact on calcium levels. Kalkwasser enables one to add calcium and alkalinity buffer to their marine aquarium.

As an economical means of adding calcium to your aquarium, doing so with a top off device as a way of replenishing water that has evaporated from your tank, this convenience kills two bird with one stone. Kalkwasser is a powerful supplement that MUST be dosed carefully, not to mention that this product is caustic and is harmful to humans if inhaled. Kalkwasser has a pH if around 12, our tanks should have a pH of anywhere between 8.0-8.4. So do the math, if you dose too much Kalkwasser you will be increasing the pH of your tanks water possibly at such a dramatic rate that fish and invertebrates will flounder, especially delicate ones like ornamental shrimp.

OK, dosing kalkwasser... the production and retention of CO2 in aquarium water plays a major role in the amount of Kalkwasser(calcium hydroxide) that gets added to tank water. The level of CO2 in the air, in the tanks water as dissolved CO2, algae growth, and production of acids by biological processes all play a role in how much calcium hydroxide is allowed into the tanks water as calcium carbonate.

As stated earlier, levels of evaporation, pH and calcium will impact the quickness and amount of the saturated Kalk solution that gets added to an aquarium. Evaporational cooling is a great way of increasing the rate that kalkwasser can keep up with the demand for calcium in each unique and diverse aquarium. Creating a strong batch of kalk solution can aid in ensuring that more calcium hydroxide gets added to your tank plus their are also two other alternatives to get the most out of the kalk solution. Either dosing the kalkwasser solution at night when photosynthesis has stopped and CO2 is able to rise, or the addition of acetic acid( household white vinegar). Vinegar represents a major source of carbon. Vinegar, glucose and calcium gluconate all work the same way and will increase the carbon dioxide in water due to the biological activities of the carbon being digested releasing carbon dioxide as a result. Vinegar is more commonly used as it is easy to find at any supermarket. The vinegar when added to the kalk solution will increase the concentration of calcium being added to an aquarium by 9% over than of the standard kalk solution alone.

It is best to dose kalk slowly and with the addition of a pH controller. The reasons for this are two fold: ability to monitor what your pH level is and be able to make changes should less than optimal changes arise before they get too out of hand. Remember that calcium should almost always be added with an alkalinity buffer which is why kalkwasser is so convenient. In tanks containing an elevated amount of calcium you will find that alkalinity levels are low and vice versa. By adding a two part solution of BOTH calcium and alkalinity you lessen the chances of these two components traveling in opposite directions. The pH monitor allows for the close monitoring of the waters pH value as a elevated pH value will cause many of the bicarbonate ions to carbonate and this over saturation of carbonate and calcium concentration will cause a milky/cloudy white color to tank water. Not to mention that a pH rise as a result of dosing kalk carelessly will cause death of livestock and this is irreversible.

Their are two main ways of adding kalk to an aquarium: either adding the solution to a top-off reservoir or to create a Nilsen calcium reactor. Either way can work to replenish water and calcium lost in the aquarium as part of this automatic water make-up system. A solenoid, float switch, reservoir container and some aquarium tubing is all that is needed to create this device. Basically what you are doing is connecting this set up to a sump. Once water has evaporated below a certain level, the float(similar to that of a toilet) activates the solenoid valve causing water/ kalkwasser solution to be added to the sump to bring the water level back up to where is belongs. Once this happens the float rises and shuts off the solenoid stopping any more water from entering the sump, possibly causing a flood or abrupt pH change.

The ideal amount of kalkwasser(dry powder) to be added to an aquarium is 1/4 teaspoon per hour(per 50gallons). Doing this every couple hours two to three times a day should suffice and not place any substantial risk on your pH level of your water. The addition of kalkwasser should enable your waters calcium and alkalinity demands to be sufficient to allow your corals and Tridacna clams to flourish as well as the ability for invertebrates to produce a strong exoskeleton for their protection.

As with any chemical, be careful and go slow. Many times we end up inflicting more damage than good by going to fast, not being knowledgeable enough or being careless. Make sure that you cover your bases, dot your i's and cross your T's when working with calcium, iodine, alkalinity, pH and salinity especially.

Happy reefing...

The Reef Aquarium Vol. Three

Science, Art and Technology

J Charles Delbeek and Julian Sprung

copyright 2005

pp. 201-220