Managing the Triad: calcium, magnesium, KH

Managing the Triad in the marine aquarium

The so-called "Triad" is made up of three chemical elements: Calcium, Magnesium and KH. The stability and correct balance of these chemical compounds are among the factors that determine a stable pH.

From the outset, constant monitoring of the Triad is recommended, using the dedicated chemical test kits available from aquarium shops.

As a general rule, please note that the correct balance between calcium and magnesium ions is closely linked to whether KH is trending up or down; therefore a "Triad in line and balanced" is essential for running a reef aquarium properly, above all for keeping corals in the SPS and LPS categories.

1. 1Calcium (Ca) for healthy coral growth
2. 2Magnesium (Mg) takes part in skeleton growth
3. 3KH carbonates and bicarbonates
4. 4Stable pH also depends on the balance
5. 5SPS and LPS corals for them the Triad is essential
6. 6Coralline algae they use magnesium too

The stability and balance of calcium, magnesium and KH are among the factors that determine a stable pH.

Calcium

In particular, the Ca (calcium) value must fall within the range 390/420 mg/l. This concentration is essential for healthy coral growth, especially for those in the SPS and LPS groups.

Note that the calcium value can rise or fall with salinity, which is why it is strongly recommended to keep the specific gravity in the range 1023/1025; in this way we give our corals more soluble calcium in the tank, bearing in mind that concentrations of about 420 mg/l are found in nature. I would like to point out that higher calcium concentrations do not make corals grow more, but could cause salts to precipitate and, as a result, tissue to recede on the corals.

1. 1Within range healthy coral growth
2. 2Same size according to the author, no extra growth
3. 3Salt precipitation forms with too much calcium
4. 4Tissue recession a possible effect on corals

The author keeps calcium between 390 and 420 mg/l: above that, the risk is salt precipitation.

Magnesium

Mg (magnesium), just like Ca, takes part in the growth of the skeleton of corals and coralline algae; its ideal range is as follows: 1300/1350 mg/l.

Whenever the concentration drops below 1250 mg/l, we will see instability in the calcium ions.

KH

KH indicates the total of carbonates and bicarbonates. It is called "temporary carbonate hardness" because the carbonates in the water turn into other chemical compounds. I personally keep only so-called stony corals, and I have found that the ideal KH value should fall within the range 6.5/8.5, also considering that natural seawater has a concentration of around 7 to 8 degrees.

pH

Whenever pH is below 8.1 we may find higher concentrations of calcium and magnesium, because the corals slow down calcification; as a result we will see that some coral branches may be elongated and brittle, or there may even be no growth at all.

1. 1Compact coral with pH within the stated values
2. 2pH below 8.1 calcification slows down
3. 3Calcium and magnesium higher concentrations are measured
4. 4Long, brittle branches or even no growth at all

If corals calcify less, calcium and magnesium stay in the water.

Summary

To sum up, here in detail are the ranges for the Triad and pH:

• CALCIUM: 390/420 mg/l
• MAGNESIUM: 1300/1350 mg/l
• KH 6.5/8.5 degrees
• PH 8.2/8.4

Calcium390–420 mg/l

350450 mg/l

Magnesium1300–1350 mg/l

12001400 mg/l

KH6.5–8.5 degrees

510 degrees

pH8.2–8.4

7.88.6

Below 1250 mg/l of magnesium, instability is seen in the calcium ions.

Corrections

If you need to correct one of the three elements of the Triad, it is strongly recommended to let 24 hours pass between one dose of buffer and the next. Of course, it is recommended to carry out the relevant tests at regular intervals: this way we will be able to assess the exact amount and requirement of the three compounds in the tank.

1. 1Test at regular intervals
2. 2Correction one dose of buffer
3. 3Wait 24 hours before the next
4. 4Reassess amount and requirement

Repeated tests tell you the exact amount and requirement of the three compounds in the tank.

author: Ciro Murino

Sources

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3. Middelburg J.J., Soetaert K., Hagens M. (2020). Ocean Alkalinity, Buffering and Biogeochemical Processes. Reviews of Geophysics 58(3): e2019RG000681.
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5. Rushdi A., Pytkowicz R.M., Suess E., Chen C.T. (1992). The effect of Mg-to-Ca ratios in artificial seawater, at different ionic products, upon the induction time, and the mineralogy of calcium carbonate: a laboratory study. Geologische Rundschau 81(2): 571-578.
6. Chan N.C.S., Connolly S.R. (2013). Sensitivity of coral calcification to ocean acidification: a meta-analysis. Global Change Biology 19(1): 282-290.
7. NOAA (2026). Ocean acidification. National Oceanic and Atmospheric Administration.