Kalkwasser aka Calcium Hydroxide.
Following on from the article about using liquid supplements to support the calcium and carbonate requirements of your corals, in this article I’m going to look at the use of Calcium Hydroxide in the reef aquarium.
Kalkwasser is a saturated solution of calcium hydroxide in water that’s used to help replenish the calcium ions required by corals to grow. The name Kalkwasser (German for lime water) reflects this method’s origin in Germany, where it was first used by one of the pioneers of the reef aquarium Peter Wilkens. Peter first described the use of Kalkwasser as a way to support the required levels of calcium and to maintain alkalinity in 1973.
The original rationale behind Kalkwasser was that calcium could be made available to the corals at the same time as evaporation losses were being made up. Its use also brings with it a few extra benefits:
It acts in the same manner as a balanced additive; although kalkwasser contains no carbonate component of its own, its addition to the aquarium forms carbonates and bicarbonates due to the combination of the hydroxide ions with CO2 in the water.
Kalkwasser helps to limit inorganic phosphate levels by precipitating phosphate from the water.
The effectiveness of protein skimming is enhanced.
The high pH helps to counteract the natural tendency of a captive reef system to acidify over time.
To sum up, you should enjoy better coral growth when using kalkwasser as you’ll be supplying calcium and carbonates in a balanced manner, while the pH of the reef will be kept at a level better suited to calcification, and phosphate (which can inhibit calcification) will be kept low.
Calcium Hydroxide is a dry, fine powder that needs to be treated with respect. It is potentially dangerous to you, your family, and your livestock, so remember to take precautions!
If you were to take a look at a safety data sheet of the type used in industry you’d see some or all of the following information:
DANGER! HARMFUL IF SWALLOWED OR INHALED. CAUSES BURNS TO SKIN AND EYES. CAUSES SEVERE IRRITATION TO RESPIRATORY TRACT.
- Personal protection: Wear suitable protective clothing, goggles, dust mask, and chemical resistant gloves.
Potential Health Effects
- Inhalation: Causes irritation to the respiratory tract. Symptoms may include coughing, shortness of breath. Can cause chemical bronchitis.
- Ingestion: Gastric irritant. Ingestion may be followed by severe pain, vomiting, diarrhoea, and collapse. If death does not occur in 24 hours, oesophageal perforation may occur, as evidenced by fall in blood pressure and severe pain. A narrowing of the oesophagus may occur weeks, months, or years after ingestion, making swallowing difficult.
- Skin Contact: Corrosive. May cause severe burns and blistering, depending on duration of contact.
- Eye Contact: Corrosive. May produce severe irritation and pain. May induce ulcerations of the corneal epithelium. Can cause blindness.
- Chronic Exposure: Prolonged or repeated skin contact may produce severe irritation or dermatitis.
- Aggravation of Pre-existing Conditions: Persons with pre-existing skin problems or impaired respiratory function may be more susceptible to the effects of this substance.
First Aid Measures
- Inhalation: Remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Call a physician immediately.
- Ingestion: DO NOT INDUCE VOMITING. Give large quantities of water. Never give anything by mouth to an unconscious person. Call a physician immediately.
- Skin Contact: In case of contact, wipe off excess material from skin then immediately flush skin with plenty of water for at least 15 minutes. Remove contaminated clothing and shoes. Wash clothing before reuse. Call a physician immediately.
- Eye Contact: Immediately flush eyes with gentle but large stream of water for at least 15 minutes, lifting lower and upper eyelids occasionally. Call a physician immediately.
OK, I’m not really trying to scare you with all this information, I just want to emphasise the importance of careful handling and illustrate why its important to keep children and pets out of the way when making up kalkwasser or recharging a kalk reactor.
Note: Too much kalkwasser, or too much added too quickly, can raise pH to unacceptably high levels causing pH shock resulting in the death of livestock.
Note: Never allow undissolved calcium hydroxide to settle out on corals as, at the very least, this will lead to localised tissue loss.
Calcium Hydroxide is strongly alkaline, when freshly made up into a saturated solution it has a pH of 12.4 with a calcium concentration of 900 mg/l. Over time, just a matter of days, this solution will react with the CO2 in the atmosphere, as it does the PH will start to drop and as the pH drops so will the amount of available calcium. The reduction in available calcium is very abrupt, by the time the pH has dropped to 12.0 calcium will be just below 200 mg/l, and by the time the pH reaches 10.0 calcium level will have plummeted to around 5 mg/l, rendering it no use whatsoever. When kalkwasser reacts with the CO2 from the atmosphere calcium carbonate is formed. Now we actually want calcium carbonate to be formed by the corals themselves through the process of calcification by which they build their skeletons, we don’t want to be just introducing calcium carbonate into the aquarium as in this form the calcium and carbon aren’t available for coral growth. This explains why you should never attempt to mix calcium hydroxide using an air stone, which would add CO2, making your calcium additive useless!
Paradoxically, the formation of calcium carbonate through contact with the atmosphere can be used to our advantage. When kalkwasser is made up for either drip dosing or is used in most kalkwasser reactors you’ll see that a milky film will develop on the surface of the solution. This film is calcium carbonate, showing where the kalkwasser has reacted with CO2. Now, as long as we don’t disturb this film and only take kalkwasser from below it, the film is acting as a barrier to the additional uptake of CO2 and is actually protecting the kalkwasser from further deterioration.
Note: Remember to always using purified water i.e. RO water when mixing kalkwasser, especially when used for evaporation replacement.
Different authorities offer differing advice about the timing of Kalkwasser additions. Many recommend dosing solely at night when the pH of the aquarium drops to its lowest level as the high alkalinity of this additive helps counteract this phenomenon; others recommend dosing at regular intervals throughout the day and night to limit spikes in both pH and calcium, keeping these levels as constant as possible.
Kalkwasser reactors are usually used as part of an automatic evaporation top up system. With an auto top up system a water level sensor or float switch in the sump (or in the aquarium if no sump is present) will activate a top up pump in response to falling water level due to evaporation, which will then pump water from a reservoir into a high flow area of the sump (or aquarium), when the sensor is back to its normal level the pump switches off. When a kalkwasser reactor is included in this system it’s placed between the water reservoir and the reef, water will then replenish the reactor at the same time as calcium rich water is added to the aquarium.
Reactors employ a device to stir the calcium hydroxide solution; depending on manufacturer this can be a stirring rod operated by a motor in the lid of the reactor, a magnetic stirrer operated by a motor below the reactor or a pump (depending on design centrifugal pump operated reactors can be a poor choice).
With a kalkwasser stirrer continually mixing the calcium hydroxide and RO water being introduced in response to evaporation losses, there is no need to make up a solution and let it clear before use. Monitor the pH of the solution being added to the reef, when it drops below 12 add another dose of calcium hydroxide to the reactor. Every month or two when the pH has fallen below 12 strip out and clean the reactor, setting it up anew.
This is the original method of dosing kalkwasser. Essentially a kalkwasser solution is made up, then allowed to drip into the reef over a period of time. Its usual to employ gravity for this form of dosing although you can also use a peristaltic pump fro the job as long as you can control the rate of delivery. A simple method is to employ a siphon from a reservoir mounted higher than the point of introduction (either in the tank or the sump), which should be a high flow area to promote rapid mixing of the solution with the aquarium water. Use airline tubing and then control the drip rate with an external clamp.
Note: If you use a tap to control the drip rate you’ll find it’ll clog more readily and will need more frequent cleaning.
I’d suggest that the first time you use this method you do so when you have a little time on your hands so you can monitor the pH of your reef as you adjust the drip rate. It’s difficult for me to prescribe a drip rate of “x” drops per minute as all reefs are different and this rate would be very much down to your pre-existing pH. As a pointer, calculate how much water is lost through evaporation each day, then set yourself a drip rate that’ll replace that volume over twenty four hours.
Mixing the Kalkwasser.
Calcium Hydroxide doesn’t readily dissolve, it’s one of those unusual compounds that actually dissolves better in cold water than hot so always use cold RO for your make up water. Add about a quarter teaspoon / 1.25 ml by volume of Calcium Hydroxide per litre of water and stir vigorously. Leave the solution to clear then decant the clear saturated liquid into your dosing reservoir. (There will be a certain amount of undissolved calcium hydroxide leftover in your mixing container that can be used to make up a further weaker solution of Kalkwasser – otherwise safely discard the residue down the drain)
Note: For best results always use freshly made up kalkwasser.
It is possible to dose calcium hydroxide manually in a way that’s both economical and quick. This is a method I’ve used successfully myself and was first described to me by Anthony Calfo. To succeed with this method you need an electronic pH meter to help you fine tune the dosage and to ensure that the pH doesn’t rise to potentially dangerous levels.
Take a small container, I use a one litre jug, and add about 200ml of cold RO water. Check the pH of your reef. Add no more than a quarter teaspoon / 1.25 ml by volume of Calcium Hydroxide to the jug and stir vigorously, pour this into an area of high water movement where it will readily mix with the tank water then use your pH meter to monitor the rise in pH. You can safely allow yourself a maximum rise in pH of up to two points i.e. 8.2 rising to 8.3 or 8.4 is fine, if it goes over 8.4 reduce the dosage the next time, if there’s no significant increase in pH then the next time you dose, add slightly more calcium hydroxide.
The recommended dosage here is for a 200 litre reef, pro rata this dosage according to the size of your aquarium then use the increase in pH as a guide to fine tuning your system’s requirements.
Which is the Best Calcium Hydroxide to Use?
Calcium Hydroxide is available from many aquarium manufacturers and suppliers, usually under a brand name. This is a common chemical with uses outside of the aquarium hobby; as a result it’s available in a number of different grades and purities. Ideally, we want a pure grade, although there are some trace elements which might be useful in the reef tank, magnesium, strontium, etc., there are just as many undesirable ones e.g. phosphate and heavy metals.
So how to choose? Unfortunately, I think all you can do is to try a few different manufacturers offerings and then stick with the one that seems to work for you. Price may be a guide, the purer forms will tend to be more expensive to purchase, cheap low grade products may contain a higher quantity of useless calcium carbonate, but unless you have access to a mass spectroscope it’ll be difficult to quantify!
Whatever product you choose, store it carefully away from children and make sure you reseal the container properly to limit exposure to CO2 from the atmosphere.
Pros and Cons.
As you’ll remember from the previous article, whatever method of supporting calcium and carbonates is used there’s no perfect solution; each method has its own pros and cons.
- One of the most cost effective ways of supporting calcium and carbonate levels in a reef.
- Can help deal with the problem of phosphate.
- Improves the effectiveness of protein skimming.
- Counters the decline in pH that can occur over time in the aquarium.
- Cancels out excessive levels of CO2 that may result from the use of a calcium reactor.
- Nothing is added to the aquarium that might accumulate over time to the detriment of the environment.
- Limited amount of calcium available making it most suited to calcium level maintenance.
- Unlikely to maintain levels in aquariums with higher rates of calcification.
- With covered aquariums there may not be enough evaporation taking place to allow effective kalkwasser dosing.
- Calcium hydroxide reactors are expensive items of equipment to purchase but the running costs are low.
- A kalkwasser reactor can constitute very real dangers to your reef if something goes wrong resulting in an overdose and a consequential rise in pH.
- Calcium hydroxide is a very caustic powder that should be handled carefully and kept away from children and pets.
As with the previous article, I’m left to conclude that ultimately the best solution to calcium and carbonate supplementation lies with the combination of more than one method, this will allow you to get the best from each, while cancelling out the deficiencies presented by any individual method.