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Kalkwasser as a Method of Calcium & Alkalinity Supplementation

Kalkwasser as a Method of Calcium & Alkalinity Supplementation

Michael Paletta - Guest Author

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

Birdsnest Coral, Pink Thin Branch - AquaculturedKalkwasser 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.
  • 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 cana be reduced when Kalkwasser is slowly added at night when pH typically drops in the aquarium.

    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 buffershould be added regularly. The dynamics of every reef aquarium changes over time so regular testing is necessary to monitor these changes.


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