Modern ReefKeeping

The use of Kalkwasser (Limewater or Calcium Hydroxide) is often debated very strongly amongst its adherents and opponents. Although I do not use it I do admit, that used properly, Kalkwasser is a safe, effective and economic supplement of both Calcium and Alkalinity in reef aquaria. Given that I do not use Kalkwasser, I have scoured my references and the web to put together the information required for you to use it safely and effectively. Let’s start.

What is Kalkwasser?
Put simply, it’s the German translation of Limewater or Chalk water. For the sake of simplicity, let’s just call it KW from here on out. KW is formed from a solution of fresh water and lime. You can buy lime as Pickling Lime at the grocery store or as KW powder at a local fish store or online. Most users consider the Pickling Lime to be more cost effective, and just as safe. The lime is Calcium Oxide; it reacts with water to make Calcium Hydroxide. Another form of lime, Quick Lime is also widely used. Its use is identical, but mixing Quick Lime with water creates heat, so some caution is advised when mixing Quick Lime.

How does Kalkwasser work?
All of the interactions and equations can be complicated but easily found in books and technical articles. For the sake of this article, I will explain as simply as possible (for my sake). Some advanced aquarists will find my explanation oversimplified, but you won’t tell them, will you? The solution is a mixture of fresh water, Calcium ions and Hydroxide ions. The addition of the Calcium ions raises the concentration of Calcium in the aquarium. The Hydroxide interacts with the dissolved CO2 in the aquarium to form Bicarbonate. The Bicarbonate and additional Hydroxide ions form Carbonate and water thus supplementing Alkalinity.

What happens if Kalkwasser is overdosed or dosed too quickly?
Adding Hydroxide without available CO2 will actually cause a reaction that can result in the loss of Bicarbonate and eventually the presence of free Hydroxide ions and elevated pH above accepted limits. The surplus Hydroxide will be exhausted as the CO2 concentration increases if KW dosing is stopped.
How is Kalkwasser prepared? Prepare a mixing container with the appropriate amount of fresh water (preferably RO/DI). Add about ½ teaspoon of lime per liter of water, cap the container and shake vigorously for a few minutes to mix thoroughly. Small amounts of additional lime can be added to compensate for the Calcium lost as Calcium Carbonate in the reaction with dissolved CO2 in the water. This amount of lime is the maximum amount that can be dissolved in water and is referred to as a saturated solution. This saturated solution will contain about 800 ppm of Calcium. Allow the solution to settle for a few hours until the solution has cleared to a slightly milky appearance and decant into a sealed storage or dosing container. The remaining sediment may be re-used for another batch, but the majority is likely to be insoluble Calcium Carbonate and of no use.

How should Kalkwasser be handled?
Both the powder and solution are highly caustic (high pH). They can cause extreme damage to your skin, eyes, and tissues of the mouth and nose. The powder is extraordinarily fine and made airborne very easily. Both safety glasses and rubber gloves are recommended for handling KW. Use large amounts of water to rinse any affected area.

How should Kalkwasser be stored?
KW solution should be stored in an airtight container to minimize its exposure to atmospheric CO2. Open to air, the solution will lose its potency very quickly. The potency of the solution has been verified level for almost three weeks in a closed plastic trash can, so a hermetic seal seems unnecessary.

How can Kalkwasser be safely dosed?
KW is generally dosed as part or the entire evaporative make up water to the aquarium at very slow rates to avoid depletion of dissolved CO2. There are a few methods available to accomplish this:
A dripper can be made or bought at stores or on online with various sizes of storage containers. The drip rate is set to not exceed an absolute maximum of ½ liter per hour of saturated solution per 50 gallons of aquarium water or the evaporation rate of the aquarium. A much lower dosing rate is recommended until Calcium and Alkalinity depletion rates are known. If drip rate is less than evaporation rate, the dripper can be complemented by an automatic top off (ATO) system. A faster drip rate can be achieved with the use of a pH controller and solenoid to stop dosing if optimal pH is exceeded.
An ATO reservoir can be used to store KW solution to be added when a low sump or aquarium level is detected. The use of power heads or other centrifugal pumps may exceed a prudent rate of KW addition to the aquarium. A peristaltic dosing pump, with a lower flow rate is more suited to the application.
A Kalkreactor or Kalkstirrer can be added into an ATO system. A surplus of lime above the saturation limit is maintained in the Kalkreactor, the solution is occasionally stirred by mechanical means and water from the ATO pump forces solution from the Kalkreactor into the aquarium when a low sump or aquarium level is sensed. The new fresh water will result in an under-saturated condition and the mechanical stirring will mix in additional lime to restore the saturated solution in the Kalkreactor. As previously stated, a peristaltic dosing pump is better suited to this method when using an ATO to dose KW.

What can be done to mitigate the high pH in the aquarium?
There are a few things that can be done to minimize the risk of high pH associated with dosing KW:
Dose Kalkwasser at night when CO2 levels are typically higher and pH is lower.
Dose CO2 to the aquarium. Dosing CO2 with a CO2 reactor and properly functioning and calibrated pH controller and solenoid valve can ensure that a prudent pH level is not exceeded while dosing KW.
Use vinegar with Kalkwasser. Distilled white vinegar can be used in two ways to help control pH. First let’s discuss how it works:
Distilled white vinegar is one of a few substances that can be used as a carbon source for this. As it is economical and available it is most convenient. The acetic acid in vinegar will break down into acetate when dosed to the aquarium. The acetate is used by some bacteria present in the water as a food source, and CO2 is formed as a bacterial product. This bears a very close resemblance to carbon source additions for the purpose of de-nitrification and has the potential to accomplish some de-nitrification as well.
Dosing vinegar separately. Vinegar can be dosed to the aquarium in conjunction with KW dosing. This can be accomplished most accurately with a dual channel pH controller and solenoids to dose each as needed to maintain pH within an established band. Flow rates should be maintained so that a malfunction will not result in a catastrophe.
Adding vinegar to the Kalkwasser solution. Up to 12 ml of vinegar can be mixed per liter of saturated KW solution. The acetic acid also has the benefit of allowing close to 1/3 more lime into solution. It is recommended to start with a dose of 3 ml per liter of solution to observe if there are any negative side effects in the aquarium. Unfortunately, my references do not include any indicators for side effects. Another reference, however, indicates that 45 ml per gallon is a safe dose to use.

What if Kalkwasser dosing is not cutting it?
There are a few avenues to take if KW dosing is not maintaining Calcium or Alkalinity at current dosing rates:
Increase evaporation in the aquarium with the use of a fan or fans if relative humidity in the house is low enough. This will allow for higher daily dosing rates.
Increase saturation level of the solution with vinegar as discussed above.
Supplement Kalkwasser with other methods such as two part solution for balanced Calcium and Alkalinity increases or Chelated Calcium without Alkalinity increases. Calcium Chloride should not be used as a means to maintain Calcium due to the high levels of Chloride introduced to the aquarium.
How do I establish an acceptable level of Calcium and Alkalinity prior to dosing Kalkwasser?
Two part solution can be used to raise both Calcium and Alkalinity to accepted levels at recommended rates.
Chelated Calcium can be used to raise Calcium levels without affecting Alkalinity.
Calcium Chloride can also be used on occasion to raise Calcium levels without affecting Alkalinity.
Water changes with a good quality salt mix can bring all aquarium parameters closer to optimal.
Using the dosing methods described above will also allow you to maintain pH when it is being depressed by excessive CO2. Calcium, Alkalinity and Magnesium levels as well as proper maintenance should be verified before employing this method of pH control.

Where do I start?
Obtain the proper equipment to responsibly use Kalkwasser.
Test your water parameters to correct levels and determine dosing rates.
Test daily to verify dosing rates.
After establishing dosing rates, test periodically to verify proper dosing and make adjustments as depletion rates change.
Maintain all parameters within accepted levels.
Happy Reefing

References:
“A Simplified Guide to the Relationship Between Calcium, Alkalinity, Magnesium and pH” By Randy Holmes-Farley in Reefkeeping Magazine
“What Your Grandmother Never Told You About Lime” By Randy Holmes-Farley in Reefkeeping Magazine
“Water Quality Guidelines for Marine Aquariums” By Bob Goemans Ph.D.
“The Reef Aquarium” By J. Charles Delbeek and Julian Sprung