Reef Advantage Magnesium

  • Concentrated, blended, ionically balanced magnesium source
  • Contains NO Ammonia
  • Vitally important in preventing ionic imbalance


Severely depleted levels of magnesium (below 800 mg/L) can cause depressed pH levels and an inability to maintain proper magnesium levels. The most frequent causes of magnesium deficiency are use of kalkwasser, frequent overdosing of a carbonate additive, or low levels in the salt mix itself. Kalkwasser, for instance, precipitates magnesium as magnesium hydroxide while excess carbonates precipitate it as magnesium carbonate. In both cases, this means that magnesium that was present in the water is now unavailable. Of the two, magnesium hydroxide and magnesium carbonate, the former is more problematic; it is extremely insoluble. Once magnesium has precipitated as magnesium hydroxide, it will never redissolve. Magnesium carbonate will redissolve; however, it does so slowly. So, while it will go back into solution, there will be a significant portion of time in which magnesium levels are depleted.

Reef Advantage Magnesium™ is a concentrated (80,000 ppm) optimized blend of magnesium, chloride, and sulfate salts designed to restore depleted levels of magnesium with minimal impact to the ionic ratios found in natural sea water. Reef Advantage Magnesium™ contains no ammonia. This is a common contaminant in every liquid magnesium supplement on the market.


BEGINNER: Use 5 g (1 level teaspoon) per 80 L (20 gallons) twice a week. Dissolve in at least 250 mL (1 cup) of freshwater. For precise dosing, use the Seachem Digital Spoon Scale.

ADVANCED: Check magnesium level, then follow addition regimen above until magnesium is adjusted to 1,200–1,350 mg/L. Each 5 g/80 L will raise magnesium by about 5 mg/L. Amount or frequency can be adjusted, but do not exceed 25 g/80 L per day. Thereafter, use as required to maintain magnesium.

EXPERT: After determining the magnesium depletion rate, set up a continuous drip system. Use the following formula to determine how much to add to your top-off water: g=vm/80 (g=grams to add to top off water, v=volume of tank in liters, m=amount to raise magnesium in mg/L). For example, if you want to raise magnesium by 10 mg/L in a 200 liter tank, then you would add (200x10)/80=25 g into the top-off water. [For reference: 1 gallon=3.8 liters, 5 g=1 teaspoon]. Notes: Use the Reef Status:™ Magnesium, Carbonate & Borate test kit to check magnesium levels.

DO NOT OVERDOSE: Excess magnesium may enhance the loss of carbonate alkalinity. Do not directly mix with any carbonate supplement. Best if magnesium & carbonate additives are added on alternate days or at least 30 minutes apart. Slight clumping of this product may be encountered but does not impact its use; any clumps will break up very easily.

Guaranteed Analysis

Amounts per 1 gram
Magnesium (Mg)(min) 80 mg

Ingredients: magnesium sulfate, sodium chloride


300g, 600 g, 1.2 kg, 4 kg

To reach your desired level use:

tspn(s) or grams

For precise dosing, use the Seachem Digital Spoon Scale

Do not exceed 25 g/80 L (20 US gallons) per day

Considerations: We recommend a magnesium level between 1200-1350 mg/L. Make large adjustments slowly to avoid overshooting intended level. Amount or frequency can be adjusted, but do not exceed 25 g/80 L per day. Dissolve in at least one cup of freshwater. Excess magnesium may enhance the loss of carbonate alkalinity. Do not directly mix with any carbonate supplement.

A: To make a stock solution, you will use the following formula for Reef Advantage Magnesium:

____(x)____ (amount you want to raise Mg each week) ÷ 5 ppm (amount that one standard dose raises Mg) = ____(a)____(how many doses you would need per 80 L to raise Mg by (x) ppm)

______(a)_____(result (a) from above) × 5g (standard amount of grams per 80L) = _____(b)______(amount of grams per 80 L needed to raise Mg by 20 ppm)

___y____ (your tank volume) ÷ 80 L (standard dose volume) = ___(c)_____ (amount of dose you need for (y))

___(b)__ (see answer (b) above) × ___(c)___(see (c) above) = ____(d)___g per week

Divide by 7 to get daily amount

For your reference: The amount of Reef Advantage Magnesium that can be successfully dissolved is 1-2 cups in 1 L of water. These are only estimations based on our findings, and results may vary in a larger volume of water.

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0636 Reef Advantage Magnesium 300 g
0633 Reef Advantage Magnesium 600 g
0637 Reef Advantage Magnesium 1.2 kg