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Kalkwasser

KALKWASSER

Kalkwasser, or lime water, is a solution of calcium hydroxide in water. Calcium hydroxide is a molecule consisting of a single Calcium atom and two Hydroxide groups. When mixed in water a portion dissolves forming kalkwasser, the stuff we are interested in, and the rest creates a cloudy suspension called milk of lime. The name "kalkwasser" comes from the German words "kalk" (lime) and "wasser" (water).

What are the Benefits of Kalkwasser?

Now that we’ve covered what it is, here is why kalkwasser is significant in the reef aquarium hobby. If you like to keep stony corals, they require both calcium and alkalinity to build their calcium carbonate skeletons. There are many ways to accomplish this. If you only have a few stony corals in your reef tank, it might be as simple as keeping up with regular water changes to maintain the necessary levels of both calcium and alkalinity. Once you get into a more densely populated aquarium perhaps with fast growing stony corals, water changes alone might not be enough to keep up.

Some hobbyists choose to supplement calcium and alkalinity by 2-part dosing of calcium chloride and soda ash. Others choose a calcium reactor that dissolves aragonite media and re-introduces calcium and alkalinity that way. Kalkwasser dosing is another method that can be done alone or in conjunction with those other methods depending on the nutrient demands of your tank.

Let’s get a little bit more specific. When Kalkwasser is added, it serves three main purposes:

Benefit 1: Supplementing Calcium
Corals and other marine organisms, such as coralline algae and some invertebrates, require calcium for the formation of their skeletons and shells. Kalkwasser is an excellent source of calcium ions (Ca2+). Calcium is a major component of their skeletons and shells, and maintaining appropriate calcium levels is crucial for their overall health and structural integrity. Natural sea water is roughly 425ppm of calcium.

Benefit 2: Boosting Alkalinity
In addition to providing calcium, kalkwasser also helps increase alkalinity in the aquarium water. Alkalinity a collection of ions that generally equate to carbonate availability in the water. The official definition is that it is the amount of acid required to lower the pH of saltwater to the point bicarbonate turns into carbonic acid. If you have more alkalinity, it can soak up more acid. Less alkalinity and you have less buffering capacity making the tank more susceptible to chemical changes.

In natural sea water, the alkalinity of the water measures around 7 or 8 dkh though most salt mixes these days mix up closer to 8 to 9 dkh. This elevated alkalinity is because in practice alkalinity tends to be the parameter that fluctuates the most and the salt manufacturers anticipate a greater demand for it in reef tanks with higher stony coral bioload.

Benefit 3: Raising pH
Kalkwasser has the added benefit of increasing pH levels in the aquarium due to the release of hydroxide ions, which helps to counteract the natural pH drop that occurs in marine systems over time. Kalkwasser is a very basic solution. It has a pH of over 12 which can be a very desirable thing for aquariums that struggle with low pH. Because it has high pH it is recommended to drip slowly into an area of high flow to quickly dissipate the solution.

Benefit 4 (sorta): Reducing Phosphates
As an aside, kalkwasser has some limited capacity to remove phosphate from the water, but it is not primarily used for this purpose. Phosphate is a common nutrient in aquariums, and in excess, it can contribute to unwanted algae growth, negatively impacting the overall water quality and the health and coloration of corals. Kalkwasser can help precipitate or bind phosphates to some extent due to its high pH. At high pH levels, phosphates are more likely to combine with calcium and form insoluble calcium phosphate precipitates. These precipitates can then be removed through mechanical filtration or by settling to the bottom of the aquarium. What we like to do is drip the kalkwasser solution into a section of our sump just before the filter sock stage so any precipitates that form are quickly caught by the mechanical filter material.

Again, kalkwasser’s ability to bind up phosphate is relatively limited, and it may not be sufficient to handle high phosphate levels on its own. Additionally, using kalkwasser primarily for phosphate control could lead to much more serious chemical problems. Just think of it as a minor perk of dosing kalkwasser.

PROBLEMS

While there are many benefits to dosing kalkwasser, no additive is perfect. There are some problems that are inherent in kalkwasser that have to be considered.

Problem 1: pH Overload
One of the primary concerns with kalkwasser is the potential to spike pH levels. Remember that kalkwasser has a pH of around 12. While it can help stabilize pH in the long run, if improperly dosed, the rapid addition of hydroxide ions can cause a temporary jump in pH levels. Sudden and significant pH shifts can stress and sensitive fish and corals.

Problem 2: Potential Precipitation
If kalkwasser is not mixed properly or added too quickly, it can cause precipitation of calcium carbonate in the aquarium. This can lead to a couple of different issues. First, it can aggressively bind up other compounds due to its high pH and lower the overall levels of those compounds below what is found in natural sea water. Second, improperly administered kalkwasser can lead to cloudy water and potential damage to pumps and equipment. If this is happening in your tank, you will notice a chalk-like deposit on your devices. Again the best methods of administering kalkwasser involve slow additions over a long period of time in an area of high water movement.

Problem 3: Calcium and Alkalinity Imbalance
One of the benefits of kalkwasser is that it is a balanced additive of both calcium and alkalinity. It is also one of the downsides if your tank’s chemistry diverges asymmetrically. For example, if your calcium is in a good range, say 425 ppm, but your alkalinity is too low and needs a boost, raising it with kalkwasser alone will be a challenge. If not carefully managed, kalkwasser dosing can result in an imbalance between calcium and alkalinity levels. Adding too much kalkwasser to boost alkalinity might lead to excessive calcium levels, and vice versa. Kalkwasser is very good for maintaining a baseline but less useful to adjust specific parameters.

HOW TO DOSE

Dosing kalkwasser can be relatively simple, but it requires some care and attention to ensure proper dosing without causing any adverse effects. When I first tried it, all I used was a 1-gallon container with a pinhole a couple inches from the bottom to slowly drip it into my sump. Fast forward about 20 years and now we use peristaltic pumps to basically do the same thing only with a lot more control and safety.

Here's a step-by-step guide on the easiest way to dose kalkwasser in a reef aquarium:

Step 1: Prepare the container
First start by selecting a container size appropriate to your system and fill it with fresh water. If you have an idea of how much water you need to top off your tank, something around that would work. A larger container is nice so you do not have to re-fill it as often but a smaller container has the inherent fail safe of only being able to do a small dose so overdosing risk is minimized.

Step 2: Prepare the Kalkwasser Solution
Add the appropriate amount of kalkwasser powder to the container. Follow the manufacturer's instructions for the correct dosage, as the concentration may vary between products.

Continue stirring until the kalkwasser powder is fully dissolved. If you used the correct amount, there should be little to no undissolved particles in the solution. If you added too much, don’t sweat it. If you happen to go over that it’s not a big deal because you aren’t going to overdose the solution. The clear solution is already saturated and any extra powder is just going to precipitate out. You would be wasting a little bit of the product but it is not the end of the world.

Step 3: Allow the Solution to Settle
After mixing, let the kalkwasser solution settle for a few hours or overnight. This step helps to ensure that any remaining undissolved particles settle at the bottom of the container, preventing them from being added to the aquarium. The clear liquid is the kalkwasser we want to administer.

Step 4: Dosing Kalkwasser
Using a dosing pump or a manual dosing container, slowly add the kalkwasser solution to the aquarium or sump. Take care not to disturb the settled particles at the bottom of the container. The best time to dose kalkwasser is during the evening or at night when the pH levels in the aquarium are lower, as kalkwasser can raise the pH temporarily.

Step 5: Monitor and Adjust
Regularly monitor the calcium and alkalinity levels in the aquarium to ensure they remain within the desired range.

Keep a close eye on pH levels, especially after dosing kalkwasser, to detect any significant fluctuations.

Step 6: Refill the Kalkwasser Solution
As the kalkwasser solution is used up, refill the dosing container with freshly prepared kalkwasser. It is possible to re-dissolve the precipitate from the past batch of kalkwasser. We like to rinse it out each time just to have better control of each dosing.

CONCLUSION

Kalkwasser is one of the tried and true techniques of maintaining water chemistry in reef aquariums. We hope this guide was helpful for hobbyists looking to build a kalkwasser dosing system for the first time. Thank you for reading and happy reefing!

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