We know that calcium is one of the major building blocks of aquatic life. As well as the fact that it is essential to maintain calcium levels as it is the primary element of exoskeletons for invertebrates and endoskeletons for vertebrates. Corals also require large quantities of calcium, which is vital in order for them to form their hard calcium carbonate skeleton. Soft corals also need some calcium, although to a much lesser extent than hard corals. If you want to know more about the importance of calcium to maintain a happy and healthy tank environment, then go read our blog piece on ‘Why Is Calcium Important To Corals’. Next, we’re going to discuss in more detail how to maintain your tank’s calcium levels at the optimal amount needed for your tank.

Brief Recap: Why Is Testing Calcium Levels Important?

By providing the right level of calcium in your reef aquarium, you are providing the fundamental building blocks needed for the survival of your corals and your invertebrates. Successful coral aquariums use the calcium naturally occurring in water, but eventually the calcium levels will deplete. Therefore, it is important to achieve the right concentration of calcium. Calcium levels should be maintained at between 400-450 mg/l, although if you have more hard corals the calcium demand will likely be higher. If your calcium concentration levels fall below this range, this will result in corals growing much slower. Too high calcium levels however will cause calcium to bind to carbonates and precipitates, rendering it inaccessible for invertebrates and deplete your carbonate hardness (KH). 

How To Maintain Correct Calcium Concentrations

The more hard corals you have, the quicker your calcium levels will drop. Maintaining the right calcium levels is accomplished by either regularly changing your tank water or by using calcium additives. In some cases you may need to use both methods in combination. Calcium supplements would be the most common option in reef aquariums if calcium levels deplete quickly.

Testing Your Calcium Concentration Regularly

If you do not test your tank’s calcium levels, it is easy for levels to sharply decline. Ideally, calcium levels should be tested once a week, or at least every two weeks. If you find consistently low calcium levels, you may wish to pursue supplementation. However, this is not a one and done fix. It is very common for aquarists to stop testing calcium levels once a calcium supplementation regimen has been established. Calcium supplementation is not a static process. It is part of an ever-changing organic mechanism where the need for calcium rises as coral colonies and other species grow and mature. Don’t forget it is also useful to observe your reef tank, test kits can fail so check the data is consistent with what you’re seeing in your tank.

Several reliable test kits are available such as the API® Calcium Test Kit or the Hanna Instruments Marine Calcium Checker HC test kit to help measure and monitor calcium levels. API® also offers an excellent alkalinity/KH test kit (KH/Carbonate Test Kit).

Reminder: Don’t forget to also test for magnesium when considering calcium. The ideal ratio is 3 parts Mg²⁺ : 1 parts Ca²⁺, this will ensure calcium is kept available and will prevent carbonate hardness (KH) from being depleted.

Calcium Additives

If your tank only has a low calcium demand, then simply changing your tank water regularly can help to boost calcium levels. It is vital to test your calcium levels before using any calcium supplement products to ensure you are not overdosing your tank. However, continuous dosing is often required if you have lots of hard corals or other organisms that take-up calcium. Here are some products that we recommend to effectively and safely increase calcium levels:

Seachem Reef Kalkwasser™

This product is very popular among aquarists, and for good reason. It’s straightforward, effective, readily available and relatively inexpensive. To use, simply add the powder to water and shake. Once the cloudy mixture has settled you can then use the clear liquid in your tank. Be careful not to add to your tank in large quantities though as this will raise your pH rapidly to excessively high levels. You might also need to add a buffer occasionally over time, as Kalkwasser lowers the alkalinity in your tank.

NOTE: Kalkwasser is caustic (corrosive), so be careful not to inhale the dust.

Calcium Chloride And Buffer

Calcium chloride with a buffer was probably the first method used for maintaining calcium levels by aquarists. This method is a simple and easy way to maintain calcium levels for a small system and does not consume lots of calcium. It is widely available and inexpensive. 

Balanced Liquid Supplements

Products like the Seachem Reef Advantage Calcium™ are a great ionic calcium option, which overcomes the problems in maintaining both calcium and alkalinity. The Reef Advantage Calcium™ also includes magnesium and strontium, meaning this will not affect your pH or deplete magnesium levels. These balanced formulas are easy to use and with the addition of dosing pumps the liquid compounds can be automatically administered. This method is the most expensive method but has become very popular.

Calcium Reactors

Using a calcium reactor automates the calcium supplementation process, making this a very sophisticated method. When used appropriately, this approach is a very reliable way of controlling calcium levels inside your tank system. It works by pumping CO₂ at a fixed rate into a chamber filled with a calcareous medium. The CO₂ lowers the pH within the chamber to an acidic level, dissolving the calcium in the water as well as the other minerals and trace elements needed for coral growth. There are relatively few issues with calcium reactors once you have made a few adjustments. These reactors can initially be expensive, but worth it in the long-term. Coralife’s CA+ Calcium Reactor is a good option.

Ideal Water Conditions For Good Coral Growth

Calcium level: 400 – 450 mg/l

Alkalinity: 7 – 10 dKH 

Magnesium: 1200 – 1300 ppm

pH: 8.2

Salinity: 35 – 36 ppt

Understanding and implementing proper calcium and alkalinity supplementation may seem difficult at first, but with proper testing and patience, keeping these compounds at their proper levels will become quite simple. If you need any further help or advice, you are welcome to contact us via our website here, or find us on Facebook, Twitter and Instagram!