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Kalkwasser as a Method of Calcium & Alkalinity Supplementation

Michael Paletta - Guest Author
Kalkwasser as a Method of Calcium & Alkalinity Supplementation
Kalkwasser - German for "limewater," it is a highly concentrated solution of calcium hydroxide in water with a high pH of 12.00+ used to supplement calcium and maintain high pH levels in reef aquariums. The popular use of calcium hydroxide or Kalkwasser, probably did more to allow us to better keep SPS corals than just about any other advancement in reef keeping. Suddenly, a whole new group of corals were being cultivated for and in the home reef aquarium.

Birdsnest Coral, Pink Thin Branch - Aquacultured Kalkwasser became the method of choice in the United States for most of the last decade, surpassing calcium chloride and buffer as the preferred calcium supplementation method. Kalkwasser has been the method of choice for European aquarists for the past twenty years, clearly suggesting the effectiveness of this method.

Kalkwasser is simply calcium hydroxide dissolved in water so it is very straightforward to use. There are many different manufacturers of Kalkwasser including Kent, Seachem, and Warner Marine, all of them having relatively the same high quality.


  • Readily available and relatively inexpensive.
  • Clean - Kalkwasser adds virtually nothing to the water that is deleterious, only calcium and hydroxide ions.
  • Raises pH for better calcification by corals - The high pH (12.00+) of Kalkwasser helps maintain a higher overall pH level in your aquarium to facilitate optimal calcification.
  • Reduces phosphate levels - Kalkwasser causes phosphate to precipitate out of solution as calcium phosphate making it biologically unavailable for algae.
  • Easy to prepare - Simply add the dry powder to water and shake. When the cloudy mixture settles, use the clear liquid as make-up water.
  • Minimizes pH fluctuations - Dramatic changes in pH can be reduced when Kalkwasser is slowly added at night when pH typically drops in the aquarium.

Reef Kalkwasser Caveat - Despite its advantages, there are some shortcomings to the use of Kalkwasser.

  • Caustic - Kalkwasser is a caustic alkaline agent so care must be taken during preparation, making certain not to inhale the dust. Kalkwasser has a very high pH (12.00+) so it should not be introduced into the aquarium in large quantities or it will dramatically raise pH to excessive levels and cause the precipitation of Alkalinity.
  • Needs to be freshly prepared - Once prepared, the Kalkwasser solution should not sit for very long or it interacts with atmospheric carbon dioxide and converts into insoluble calcium carbonate. Kalkwasser solution should be prepared daily before it is added to the aquarium.

The use of Kalkwasser is a very good method of supplementing calcium for small to medium sized reef aquariums. For best results, Kalkwasser should be trickled in at night and a buffer should be added regularly. The dynamics of every reef aquarium changes over time so regular testing is necessary to monitor these changes.

Methods for Dosing
  1. Kent Marine AquaDose
  2. Dosing Pump (SP-3000 Dosing Pump) used in conjunction with a pH controller.

Part 3 of 6. Continue reading:

Part 1
Part 2
Part 3
Part 4
Calcium Chloride
Part 5
Balanced Supplements
Part 6
Calcium Reactors

Michael Paletta is the author of two books, "The New Marine Aquarium" and "Ultimate Marine Aquariums," and has acted as a consultant with the National Aquarium in Baltimore and the Pittsburgh Zoo Aquarium.


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