What is magnesium?
Magnesium is the second-most abundant cation found in natural seawater. Magnesium is essential for the efficient assimilation of calcium by marine invertebrates.
Why test for magnesium?
Without the correct levels of magnesium, corals and invertebrates cannot properly or efficiently utilise calcium for the formation of their shells and growth of skeletons. Sufficient magnesium also prevents precipitation of calcium and carbonate ions, ensuring bioavailable calcium and a pH stabilising effect. As magnesium tends to deplete with the age of the water, monitoring the magnesium frequently is the only reliable method to determine the concentration present in the water.
What is the correct level of magnesium?
The average magnesium level in natural seawater is 1300-1400 mg/l. Equally importantly, the correct ratio between magnesium and calcium should be achieved. The concentration of magnesium should be 3 times that of calcium (e.g. a magnesium to calcium of 3:1).
What to do if the magnesium level is wrong?
If the magnesium concentration in your aquarium is wrong, partial water changes using a good quality reef salt is recommend to help re-establish the correct magnesium concentration. It is also important to check the calcium and KH as the three are correlated. If the magnesium is incorrect, calcium and KH are also likely to be wrong.
How to test for magnesium?
N.B. To avoid cross-contaminating the titrating reagent (Mg-3), do not return the small quantity of the titrant left in the syringe back into the bottle at the end of the test. After use, clean and dry the syringe, tip and titration vessel with mineral-free water (such as RO water, if available) to ensure the accuracy of subsequent tests.
Q: Why do I run out of 1 reagent before the other(s)? A: We fill our test kit reagent bottles to a minimum amount before they are put through a vigorous QC regime. This means that the vast majority of bottles will in fact be overfilled by varying amounts meaning that the reagents may well run out at different rates but you should be able to carry out at least the number of tests stated on the packaging.
To find out more about water quality and parameters in saltwater aquariums, click here.
For common frequently asked questions, click here.
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