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Understanding Calcium & Alkalinity

Date Published - 5th April 2017 - Published by - iQuatics Ltd

Calcium and alkalinity are two vital aspects of your reef tank. Calcium is a crucial part of a vast majority of organisms in your tank since it helps their growth. Alkalinity is essential for ensuring that the pH level of your tank is around the 8 – 8.4 range when keeping a reef tank.


Calcium is essential to growing a happy healthy reef tank. Calcium forms the skeleton of a lot of organisms including: corals, algae and molluscs. The general consensus is that the amount of Calcium that should be found in your tank should be above the amount that is found in regular seawater, this rule particularly applies for high demand tanks. In order to increase the concentration of Calcium in your reef tank you will need a form of Calcium supplementation of which there are several.

Calcium Supplements

All supplements that are available are going to require constant care and are a big commitment for your tank. The first is 2-part liquid supplement which both adds calcium and trace elements whilst the other is an alkalinity component. These in particular, require attention since they elevate salinity. Like the 2-part liquid supplement, there are also liquid calcium supplements, these obviously increase calcium but your alkalinity level will need to be consistently monitored.

Kalkwasser is another supplement, this one is a form of lye which is mixed in with water to create a calcium-rich solution. By far the most complex method is a calcium reactor, this however, is a very popular method at present for high demand systems. The final supplement is a dry Calcium/ Alkalinity products. These are supplements that are split into two parts and control the calcium level.


There are a variety of alkalinity forms but when it comes to your reef tank it is best to focus on ‘Total Alkalinity’. Total Alkalinity in your reef tank should be in the 8- 8.4 range. Alkalinity is important since a lot of organisms in your tank such as coral, for example, accumulate calcium carbonate in their bodies which can only be done by consuming the water they inhabit. Measuring calcium carbonate is incredibly difficult so instead, measure alkalinity amounts as an easier alternative.

A Final Word

In conclusion, despite the slightly mind boggling jargon that can be associated with both Calcium and Alkalinity it is truly an essential for these two things to be prioritised if you want to run a successful reef tank!

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