Reef Advantage Calcium

  • Concentrated, powder ionic calcium
  • Maintains magnesium and strontium
  • Can be added directly to aquarium

Reef Advantage Calcium™ is a non-caustic (pH 8.3–8.6) optimized blend of ionic calcium designed to restore and maintain calcium to levels found in natural seawater. Calcium and carbonates are essential to all coral growth. If either becomes deficient, coral growth will cease, followed by a rapid decline in coral health.

Reef Advantage Calcium™ also includes magnesium and strontium in amounts proportionate to typical utilization ratios (100:5:0.1, Ca:Mg:Sr). This allows one to maintain these two important elements while maintaining calcium. Unlike limewater (kalkwasser), Reef Advantage Calcium™ does not have a caustic pH and will not deplete magnesium. Used as directed, it will not deplete alkalinity.

Sizes: 250g, 500 g, 1 kg, 4 kg


Use 5 g (1 level teaspoon) per 150 L (40 US gallons) twice a week. For precise dosing, use the Seachem Digital Spoon Scale. Dissolve in at least 250 mL (1 cup) of freshwater. Check calcium every 2 weeks and adjust amount or frequency accordingly.


Check calcium level (use Reef Status™ Calcium to test magnesium levels), then follow addition regimen above until calcium is adjusted to 380–420 mg/L. Each 5 g/150 L will raise calcium by about 12 mg/L. Quantity or frequency can be adjusted, but do not exceed 10 g/150 L per day. Thereafter, use as required to maintain calcium.


After determining the calcium consumption rate, set up a continuous drip system. Use the following formula (or skip the math and use our Dosage Calculator) to determine how much to add to your top-off water: m=vc/400 (m=grams to add to top off water, v=volume of tank in liters, c=amount to raise calcium in mg/L). [For reference: 1 gallon=3.8 liters, 5 g=1 teaspoon].

DO NOT OVERDOSE: Excess calcium may enhance the loss of carbonate alkalinity. Do not directly mix with any carbonate supplement. Best if calcium & carbonate additives are added on alternate days or at least 30 minutes apart.

To reach your desired level use

g ( tspn)

Do not exceed 10 g/150 L (40 US gallons) per day


Use Reef Status™ Calcium to test calcium levels.

We recommend a Ca level between 380-420 mg/L with an alkalinity between 3-6 meq/L (8-17 dKH). It is advisable to make large adjustments slowly to avoid overshooting intended levels or shocking corals and inverts. Each 5 g/150 L will raise calcium by about 12 mg/L.


Do not exceed 10 g/150 L (40 US gallons) per day. Excess calcium may enhance the loss of carbonate alkalinity. Do not directly mix with any carbonate supplement. Best if calcium & carbonate additives are added on alternate days or at least 30 minutes apart.

A: Reef Advantage Calcium™ is a concentrated calcium supplement capable of raising 20 gallons of water by 25 ppm of calcium with only 1 teaspoon. The biggest advantage is the ability to know exactly how much product to add in order to achieve any calcium level while restoring other essential ions. As an added bonus it mixes to a pH of 8.3 to 8.6 so you can forget about the pH battles associated with other calcium supplements. Additionally, it also contains strontium and magnesium ratios proportional to typical depletion rates. If Reef Advantage Calcium™is used to maintain calcium, then other strontium and magnesium supplements are not necessary.

A: Our Reef Advantage Calcium™ and Reef Calcium™ are completely different calcium supplements. Reef Advantage Calcium™ is an ionic calcium that is very concentrated and very economical to use. Reef Calcium™ is an organic calcium complex that is very readily available. The calcium in this product is bound to an easily metabolized carbohydrate, hence it being very available and your corals do not have to expend as much energy to use this form of calcium. In using these products together, I would consider Reef Advantage Calcium™ your primary calcium supplement and Reef Calcium™ as your secondary calcium supplement.

A: Reef Complete® is the liquid version of Reef Advantage Calcium™. They are both ionic calcium supplements that also provide magnesium and strontium in typical utilization ratios. Since they both are the same, it simply comes down to whether you prefer liquids or powders. I personally prefer liquid because they are simple to dose and no pre-mixing is necessary. That being said, powders can be very economical. Reef Calcium™ is an organic calcium meant to help maintain calcium levels in a system, while Reef Advantage Calcium™ and Reef Complete® are meant to raise calcium levels in the system. Reef Calcium™ is a poly-gluconate calcium that will provide more calcium to the system without the corals having to expend any extra energy, thus increasing growth and maintaining calcium levels. Reef Calcium™ typically will not be used to raise Calcium in the system, but rather to maintain calcium that is already existent in ideal levels. If levels are not in the ideal range, we would recommend that you use Reef Complete® or Reef Advantage Calcium™ to boost calcium levels.

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

____(x)____ (amount you want to raise calcium each week) ÷ 12 ppm (amount that one standard dose raises calcium) = ____(a)____(how many doses you would need per 150 L to raise calcium by x)

______(a)_____(result (a) from above) × 5 g (standard amount of grams per 150L) = _____(b)______(amount of grams per 150 L needed to raise calcium by (x) ppm)

____y____(your tank volume) ÷ 150 L (standard dose volume) = ___(c)___ (amount of dose you need for (y))

___(b)___ (see (b) above) × ___(c)___(see (c) above) = ____(d)_____ per week

Divide by 7 to get daily amount

For your reference: The amount of Reef Advantage Calcium™ that we have dissolved successfully is 1tsp in 25-30 mL of liquid. That means that for 1 L of RO/DI water you should be able to successfully dissolve 33-40 tsp (165 g-200 g) of Reef Advantage Calcium™. These are only estimations based on our findings, and results may vary in a larger volume of water.

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Amounts per 1 g
Calcium (Ca) (min) 335 mg
Calcium (Ca) (max) 347 mg
Magnesium (Mg) (min) 17 mg
Strontium (Sr) (min) 0.34 mg

Ingredients: Calcium Chloride, Magnesium Chloride, Strontium Chloride

Download Safety Data Sheet (SDS)

CAUTION: Causes serious eye irritation. Keep out of reach of children. Avoid contact with skin.

0316 Reef Advantage Calcium 250 g
0313 Reef Advantage Calcium 500 g
0317 Reef Advantage Calcium 1 kg