Reef Kalkwasser

  • Very pure calcium hydroxide
  • Ideal for increasing calcium in top-off water
  • Increases pH with no impact on carbonate alkalinity


Reef Kalkwasser™ is a pure calcium hydroxide with unsurpassed purity and solubility characteristics. Calcium hydroxide is used to prepare limewater (kalkwasser) solutions that will maintain calcium concentrations at natural seawater levels. Kalkwasser solutions maintain calcium directly and carbonate alkalinity indirectly. However, its capacity to perform these functions is dependent on evaporation rate and CO2 concentration. If these two factors are insufficient you can provide additional calcium with Reef Advantage Calcium™, Reef Complete™, or Reef Calcium™, and carbonate alkalinity with Reef Builder™ or Reef Carbonate™ (do not mix these directly with a kalkwasser solution).

While Reef Kalkwasser™ is a high purity and economical limewater mix, the beginner, or someone with not as much time to devote to their system, may prefer to use other less involved methods for maintaining proper ionic concentration levels.


Never add this product directly to the tank. Add 3 g (1 teaspoon) to 4 L (1 gallon) of water and mix to dissolve. If using pure water, a fully saturated solution is prepared by adding 6 g (2 teaspoons) to 4 L (1 gallon). Drip this solution into tank. Monitor pH and carbonate alkalinity. Adjust rate of addition to maintain a stable pH (8.3–8.4). Notes: Adding 4 L (1 gallon) of a saturated kalkwasser solution to 150 L (40 gallons) will raise calcium by 24 mg/L. Always use the clear supernatant (top solution) only and do not allow undissolved material to enter the aquarium. Keep this container tightly closed when not in use and minimize solution/air contact to avoid calcium carbonate formation/precipitation.

CAUTION: Causes Burns. Keep out of reach of children. Wear suitable gloves and eye/face protection. Avoid contact or breathing dust. Do not eat or get in eyes. In case of contact, flush area with water for 5–10 minutes. In case of eye contact, wash eyes with water immediately (5–10 minutes) and seek medical attention.

Guaranteed Analysis

Amounts per 1 gram
Calcium (Ca) (min) 535 mg
Calcium (Ca) (max) 540 mg
When mixed as directed (saturated kalkwasser solution):
Calcium (Ca) (min) 0.9 mg
Calcium (Ca) (max) 0.9 mg

Ingredients: calcium hydroxide


250g, 500 g, 1 kg, 2 kg

A: It is very likely that the excess calcium hydroxide (kalkwasser or lime water) that has settled to the bottom will not dissolve and will have to be discarded. The longer it sits, the more likely the hydroxide will convert the CO2 in the water to carbonate. This carbonate will form a precipitate with the calcium (calcium carbonate) and will not dissolve.

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0393 Reef Kalkwasser 250 g
0397 Reef Kalkwasser 500 g
0398 Reef Kalkwasser 1 kg