Introduction

Magnesium should be maintained at between 1250 to 1400ppm. Magnesium is important as it keeps the calcium and alkalinity levels high in seawater. These are highly dissolved and if it wasn't for magnesium would precipitate out (form solids, coming out of the sea water).

For further information click on this link:
http://reefkeeping.com/issues/2006-07/rhf/index.php.

If your magnesium level is low then this can in turn result in fairly rapid changes in calcium and alkalinity. So it is important to keep your magnesium level with this range. After the initial few months, magnesium levels in the aquarium do not change rapidly and only require an infrequent adjustment. However you need to watch the magnesium levels in your newly prepared salt water. As frequent water changes, with a low level of magnesium can slowly dilute the magnesium in the tank. It is therefore prudent to check your newly prepared salt water before conducting the water change and make any adjustments.

Increasing your magnesium level in your tank is fairly easy and can be done by using an "off the shelf" liquid additive. For small tanks/adjustments this can be effective, however for the larger tanks/adjustments then it is more cost effective to add a mixture of Epsom Salts (Magnesium Sulphate) and/or Magnesium Chloride. The preference is to use a mix of both Magnesium Sulphate and Magnesium Chloride as this maintains the balance correctly.

If your magnesium levels are high, then test a fresh salt mix to see what the magnesium levels are, if unusually high then consider changing your salt brand. Carrying out regular water changes with a salt containing less magnesium than your tank level, will gradually bring the magnesium levels down.

Application

Using the calculator below find out the dosage amount. Weigh the dosage carefully.

Mix the dose with 1 to 2 litres of RO water. Stir thoroughly to dissolve the salts until the mixture is clear. Then drip the mixture slowly over the course of several hours into a high flow area of the tank such as weir, sump return area etc.

Due to the sensitivity of marine organisms, it is not advisable to raise magnesium by more than 50 ppm per day.

When increasing magnesium, it is not advisable to perform other supplements at the same time.

If you are unsure about anything discussed above, raise a thread in the 'Help and advise' or 'Chemistry' areas of the forum.