Kalkwasser Instructions

by Bulk Reef Supply on May 14th, 2012

Kalkwasser, also known as Kalk or Limewater, is arguably the easiest and cheapest Calcium and Alkalinity solution for low to medium demand tanks, and is our recommended method for those new to the hobby. Kalk also has the benefit of raising pH and is often used with an auto top off system or slowly dripped into the tank.





  • 3 clean 1 gallon jugs with caps
  • 3 gallons of RO/DI or filtered water
  • Magic marker for labeling containers
  • Clean 1 gallon (or larger) bucket or bowl
  • Funnel
  • Household measuring spoons (Teaspoon)
  • Household measuring cups
  • Mixing spoon



Raising Calcium and Alkalinity to proper levels

Before dosing Kalkwasser it is necessary to test and raise calcium and alkalinity levels to their correct levels. This step must be done with Calcium Chloride and Sodium Bicarbonate. Kalkwasser should not be used for this because, in large doses, it will significantly raise pH.



Mixing the Solutions




  • Measure 2 ½ cups of Crystalline Calcium Chloride Dihydrate and add to 1 gallon jug
  • Fill jug about 4/5th with RO/DI water, secure cap and shake until dissolved
  • Fill the remainder of the jug with RO/DI or filtered water
  • Label "Calcium" and let sit for several hours before use




  • Fill one of the gallon jugs about 4/5th with RO/DI or filtered water and pour into empty bucket or bowl
  • Measure out 1 ⅛ cups of Sodium Bicarbonate.
  • While stirring the water slowly pour the Sodium Bicarbonate into the bucket or bowl.
  • Once dissolved, use the funnel to pour the solution into one of the empty gallon jugs
  • Fill remainder of jug with water, cap and label "Alkalinity."
  • Let solution sit for several hours before use.


*Note* Mixing the alkalinity portion directly in the jug is more difficult to dissolve and may result in clumps forming at the bottom. If clumps occur warm the jug in a sink of hot water and shake vigorously.


Dosing Calcium & Alkalinity


  • First test calcium, alkalinity and magnesium levels and adjust to their correct points if needed. Levels must be at the right points before beginning daily dosing. Use the BRS Reef Calculator to determine proper Calcium Chloride, Sodium Bicarbonate and Magnesium amounts to adjust calcium, alkalinity and magnesium.

    Follow the calculator’s instructions when adding to tank - Be sure to dose each solution separately and slowly to high flow areas of the tank. This is especially important when dosing the Alkalinity portion as a temporary increase in pH will occur. NOTE: When adding Alkalinity white flakes or a cloud may appear. This is normal and happens because the solution is highly concentrated. It will dissipate as the solution spreads throughout the tank. Just be sure to add the dose slowly to a high flow area.



Raising and maintaining Magnesium levels (Optional)

Maintaining Magnesium is important because it plays an essential role in keeping levels of calcium and alkalinity stable.


  • Add included silver pouch of Magnesium Mix to 1 gallon jug
  • Fill this jug about 4/5th with RO/DI or filtered water, cap and shake until dissolved
  • Fill the remainder of the jug with water, cap and label "Magnesium." Let the solution sit for several hours before use.
  • Test Magnesium levels and select the "Gallon of Magnesium Solution" on the BRS Reef Calculator to determine the dose.
  • Be sure to follow the directions in the calculator to avoid overdosing.
  • After the initial dose you will find that magnesium levels will drop slowly and in most tanks only require an adjustment every few months.



Maintaining new levels with Kalk using an Auto Top Off System

The typical Auto Top Off setup uses a container to hold the Kalkwasser and a float switch or valve that activates a pump to add it to the tank as water evaporates. The maximum amount of Kalk that can dissolve in fresh water is 2 teaspoons per gallon of water. Once you find that this maximum no longer maintains your tanks levels, consider switching to Two Part. Be careful not to add too quickly or overdose. We suggest using a pH controller on your Auto Top Off to prevent overdoses.


  • Using the table below, add the recommended amount of Kalk to your Auto Top Off container. Keep in mind that gallons refers to the volume in the auto top off container, not the water volume of your tank.
  • Test Calcium and Alkalinity levels every few weeks and adjust the amount of Kalk as necessary until levels are maintained.



    Recommended Kalkwasser Starting Points

    Fish only with live rock A few corals Mix of LPS and a few SPS
    ½ Teaspoon per gallon of fresh water* 1 Teaspoon per gallon of fresh water* 2 Teaspoons per gallon of fresh water*
    *This refers to water volume in the top off container only. NOT the water volume of the entire system.*