Reef Calcium

  • Liquid organic calcium source
  • Maintains calcium and accelerates coral growth
  • Concentrated (50,000 mg/L)

Reef Calcium™ is a concentrated (50,000 mg/L) bioavailable polygluconate complexed calcium intended to maintain calcium in the reef aquarium without altering pH. Additionally, polygluconate contains no nitrogen or phosphorous, thus it is biologically impossible for it to lead to algae growth in a properly maintained reef system.

Polygluconate complexation confers several benefits: it increases the bioavailability of the calcium, it provides a rich source of metabolic energy to help maintain peak coral growth, and it prevents calcium precipitation/alkalinity depletion.

Reef Calcium™ utilizes a chained organic calcium rather than an ionic calcium. When a coral absorbs a molecule into its tissue, it uses the same amount of energy regardless of molecular size. However, charged molecules require more energy. When an uncharged molecule of Reef Calcium™ is absorbed, the coral acquires multiple calcium atoms as well as an easily metabolized carbohydrate with less energy expended than it uses for ionic calcium uptake. Therefore, at lower calcium levels, corals can still take in as much calcium through our organic chains as they would at much higher levels of ionic calcium.

Reef Calcium™ may be used alone to maintain calcium but will provide enhanced levels of coral growth when used in conjunction with an ionic calcium supplement (Reef Complete®, Reef Advantage Calcium™). Reef Calcium™ is intended to maintain calcium levels; if calcium becomes seriously depleted one should either perform a water change or use an ionic calcium supplement to restore the depleted level of calcium.

Sizes: 100 mL, 250 mL, 500 mL, 4 L

Add 1 capful (5 mL) per 80 L (20 US gallons) twice a week. You can increase the amount or frequency based on growth response but do not exceed 3 capfuls per 80 L (20 gallons) per day. Each capful will raise calcium by about 3 mg/L.

Notes: Use the Reef Status™: Calcium test kit to measure calcium. It is not necessary to exceed 380 mg/L total calcium when using this product. Color and clarity may vary between lots.

To reach your desired level use

mL ( caps)

Do not exceed 15 mL per 80 L (20 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 level or shocking corals and inverts.


Do not exceed 15 mL per 80 L (20 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: No. This is a faulty assumption based on the premise that polygluconate is the same as glucose. Polygluconate is not a sugar any more than cellulose is a sugar (it's a polysaccharide). Cotton is almost pure cellulose, if you saw some cotton would you consider that to be a sweet treat? Polygluconate can be broken down into gluconate. The corals also can break it down and use it as a carbon source, as does your biological filter (some people even add ethanol to their system to "jump start" their biofilter... it's the same principal). In this vein, one side effect sometimes seen when using Reef Calcium™ is a dip in nitrates (if they were already up of course). The use of Reef Calcium™ presents no more of problem with respect to adding too much organics than does feeding your fish. Gluconate is a carbohydrate; fish foods also contain carbohydrates, either directly or within cellular DNA/RNA (DNA and RNA both contain cyclic carbohydrates (5 membered furanose rings) as their backbone). So the risk of a problem from Reef Calcium™ is equivalent to the risk from using fish food. The key here is that Reef Calcium™ is not being added in excess to what the tank can support. When the calcium is utilized the carbon component is also necessarily utilized and will not build up. If you overfeed your fish you're going to cause a problem, and if your overuse Reef Calcium™ you can run into a similar problem.

A: In chemical terms, it is a complex of ionic calcium and polygluconate. The end result for the hobbyist is that you get a more stable, more concentrated form of calcium than can be found in kalkwasser solutions (175 times greater than KW). It provides a uniary source of calcium and carbon which has no impact on pH and is more bio-available and readily absorbed by calcerous animals. For those who are even more curious, read on ... Polygluconate is a long chain polymer of gluconic acid (the polymerization occurs under high heat during product production). This creates essentially a long carbon backbone with numerous hydroxyl groups that can participate in complex formation with ionic calcium. In a complex the lone pair electrons on the hydroxyl oxygens are shared between the oxygen and calcium, essentially bonding the two together. When two hydroxyls participate this neutralizes the +2 charge on the calcium, creating an overall charge neutral species. In a chelate there are many more bonds from the same molecule to the calcium such that the calcium is surrounded (like a claw, "chelate" is greek for "claw" btw) and is held much more strongly owing to the multiple interactions. Because cellular tissue is essentially "greasy" it does not like to allow charged species to pass through it passively (e.g. oil and water don't mix). Thus the requirement that special enzymatic mechanisms be present to transport the required cations across the cellular membrane. By masking the charge on the calcium, the calcium polygluconate species is able to passively enter cells through osmosis. The cells and hence the organism as a whole doesn't have to "work" as hard to get the calcium it needs. The resulting benefit to all of this is that because the calcium complex can be more easily used one can either get enhanced growth at the normal calcium level of 400-420, or one can maintain calcium at 370-380 and not encounter any declines in growth (while still seeing growth, just not as rapid as at the higher levels). This is because the level of calcium complex that is present at the prescribed dosing is essentially equivalent to a much larger level of ionic calcium in terms of how much can be used within a given time frame.

A: Reef Calcium™ is no longer chelated, it is a complexed calcium. Also, most tests on the market will work with our Reef Calcium™, with no issues.

A: This is normal for this product and is of no consequence. The crystals should go back in to solution if shaken. This product, like the vast majority of our line, is designed to have an indefinite shelf life. This particular product may need occasional shaking.

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.

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Amounts per 1 g
Calcium (min) 50 mg
Calcium (max) 52 mg

Ingredients: calcium gluconate

0355 Reef Calcium 100 mL
0356 Reef Calcium 250 mL
0353 Reef Calcium 500 mL
0358 Reef Calcium 2 L