Additives – The Essentials!

It is essential to replenish calcium, carbonate, and magnesium as they are consumed by the corals in your aquarium.   Partial water changes are needed to re-balance the many trace elements found in seawater, but some elements are used more quickly than water changes can replenish them.  This is a very basic guide to maintaining the essential water parameters of a reef tank.  While it is typically stony corals that are responsible for the consumption of the elements below, it is very important to test and maintain them in any reef aquarium.

The Essentials


Also commonly referred to as “carbonate hardness”,  “KH”, or  “alkalinity”.  Carbonate hardness is essential for the health and growth of the invertebrates in your tank.  It is also plays a large part in the stability of your pH.  It is consumed by corals and must be tested for and added on a regular basis.  The most common unit for measurement of carbonate is dKH.  Aim for 7-12dKH.


Another important one!  Calcium is consumed by corals as they grow their calcium carbonate skeletons.  It is measured in ppm (parts per million).  Aim for 420-450 ppm.


Magnesium is frequently overlooked.  It is an essential component of coral skeletons, and plays an important role in the balance between calcium and carbonate.  If you can’t seem to balance your calcium and carbonate, low magnesium is a likely cause.  Aim for 1300-1320ppm.


Products to raise and maintain the elements listed above are available in powdered or liquid form.  Powdered additives will need to be dissolved in water before adding them to the aquarium.  Always follow the directions on the packaging and be sure not to add to exceed maximum daily dosage.  Raising these parameters too quickly can be stressful to your tanks inhabitants.

Remember that the consumption of calcium, magnesium, and carbonate will change over time.  Adding more corals or increasing light (since light is directly related to growth rate in photosynthetic corals), will increase consumption.  As corals grow larger, consumption increases.  Test your water, and adjust your dosing as necessary.

Getting the best growth from your corals requires stability in your calcium, magnesium, and carbonate levels.  Dosing smaller amounts more frequently avoids the problem of rapid swings in concentration.

The Two Part

The easiest way to maintain calcium, magnesium, and carbonate is to use a two part product.  Two part products include these elements in the same ratio as they are used by corals, so we can take the balancing act out of dosing.  Two parts are usually sold as a set of two bottles.  One bottle will contain calcium and magnesium, and the other bottle will contain the carbonate.

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