The Salifert Magnesium Test Kit is a reliable and precise tool designed to help aquarists accurately monitor magnesium concentrations in their aquarium water. Magnesium plays a crucial role in maintaining the chemical balance of marine environments—it stabilizes calcium and alkalinity levels, supports coral growth, and contributes to the overall health of reef ecosystems. This test kit provides an easy-to-use colorimetric method that delivers clear results in measurable increments of approximately 30 mg/L, allowing hobbyists to detect even small variations in magnesium levels. Suitable for both reef and saltwater aquariums, the Salifert Mg Test Kit offers around 50 tests per package, making it an economical choice for routine monitoring. Its straightforward procedure, quick reaction time, and high level of accuracy have made it a trusted option among marine enthusiasts who seek to maintain stable and optimal water parameters for thriving corals and invertebrates.

Magnesium is present in NSW in a fairly high concentration (1300 - 1400 mg/L). Magnesium is an essential part of chlorophyll, which is necessary for photosynthesis. Without photosynthesis plants, including algae and the corals, which we usually have in our aquariums, would not be able to live.

Magnesium has another important function since in fact makes maintaining the correct combination of calcium concentration and alkalinity or carbonate hardness possible.

The explanation is as follows. Calcium forms with carbonates and bicarbonates an insoluble compound called calcium carbonate. Yes this is indeed an important building stone for corals and calcareous algae but then it should be formed by biological processes and be deposited at the right place. Therefore formation of calcium carbonate by chemical processes should be avoided.

Even without biological interference calcium carbonate would be formed and would deplete calcium and alkalinity or carbonate hardness without fulfilling any function. In fact it will scavenge many important trace elements as well lowering the trace element concentration.Magnesium slows down this negative process. The lower the magnesium concentration the faster this negative process will take place and also at a much lower calcium and alkalinity/carbonate hardness value.

Maintaining a correct magnesium concentration is therefore very important and is indirectly responsible for fast coral and calcareous algae growth by virtue of making the maintenance of correct calcium and alkalinity figures possible.

Magnesium is depleted by algae and is also depleted by the use of excessive kalkwasser and by going far beyond natural calcium and alkalinity and pH values.

There are also certain brands of salt, which have or had a dramatically low magnesium content. Use of such a salt will result in permanent problems with calcium and carbonate hardness values.

Conclusion:

The measurement of magnesium and taking corrective measures are justified. Magnesium additives should be such that no ionic imbalance is created. Furthermore many magnesium salts contain sufficient amounts of ammonia to upset biological balances. Very high-grade magnesium salts are therefore required.

Magnesium is an element which was neglected for a long time. The magnesium content of some aquariums appears to be rather low when tested. Corrective measures have to taken for a balanced reef system.

The Salifert magnesium test is very straightforward and does not suffer from calcium and strontium interferences when within certain bounds. It measures in sufficient accurate steps of 30 mg/L with a sharp color change. The kit can perform approx. 50 measurements.

The Salifert liquid-magnesium additive does not imbalance the system and is ultra pure. Salifert was the first in offering such an additive. A more economical version suitable for a one time major correction is the Salifert Magnesium-powder

Principle & Chemistry of Magnesium Test Kit (Mg)

• This is a colorimetric reagent test: you add the sample water plus reagents, allow a reaction, and read a color change that correlates to magnesium concentration.

• The reagents react with Mg²⁺ ions to form a colored complex (or shift color intensity) whose shade shifts with concentration.

• Because of the discrete incremental steps (30 mg/L), fine distinctions smaller than that increment may not be well resolved.

Typically, the Salifert Magnesium Test Kit comes with:

• Reagent solution(s) (one or more bottles)

• A test vial / tube

• Measuring droppers or syringes for accurate dosing

• Instruction manual + a color comparison chart

• Packaging to hold all components

• Enough reagents to perform ~50 tests

Strengths

• Good coverage for reef needs: Magnesium is a key parameter in marine aquaria (affecting coral growth, stability of calcium/alkalinity balances). The kit gives a usable tool to monitor that.

• Cost-effective: At ~50 tests per kit, it’s relatively economical for regular monitoring.

• Discrete increments: The 30 mg/L step provides clarity in reading (less ambiguity between very close values).

• Relatively quick: Users report it gives results fairly rapidly (no extremely long wait times).

Limitations

• Limited resolution between increments: Because it only steps in ~30 mg/L increments, you cannot precisely distinguish values in between those steps.

• Subjective color matching: As with all visual reagent tests, slight differences in lighting, tube clarity, or angle can influence how the color is perceived.

• Interference / contamination risk: If test vials or reagents are contaminated, or if there are interfering ions or organics, results may be skewed.

• Not “laboratory precision”: Suitable for hobbyist/reef use, but not as precise as laboratory or instrumental methods (e.g. ICP, photometric analyzers).

• Freshwater limited relevance: In many freshwater systems, magnesium (though important) is less often a limiting / closely monitored parameter; thus the test’s marine focus is more common.

To get reliable readings from your Salifert Mg kit:

1. Use clean, scratch-free vials / tubes — scratches or residue scatter light.

2. Rinse test vial with aquarium water before taking sample to avoid dilution or contamination.

3. Measure reagent volumes exactly using the supplied droppers or syringes.

4. Mix gently yet thoroughly to ensure full reaction. Avoid foam or bubbles.

5. Observe recommended wait times — don’t read too early or too late.

6. Read under consistent lighting (neutral daylight or bright white light, avoid colored or tinted bulbs).

7. Compare to color chart at eye level and from a consistent angle.

8. Always test the same way (same batch, same timing, same method) to reduce variation.

9. Record water conditions (temperature, salinity, alkalinity, calcium, pH) alongside Mg reading to help contextualize it.

10. If your sample is too dark (off-chart), you may need to dilute with deionized water and correct the result proportionally.

Interpretation 

• Magnesium role: In reef aquaria, magnesium helps buffer and stabilize calcium and alkalinity; it ensures proper ionic balance so that calcium and bicarbonate ions don’t precipitate. It also supports coral health and growth.

• Target ranges: Reef keepers often aim for magnesium in a range of ~1250 to 1400 mg/L (ppm) depending on specific protocols and system goals.

• If magnesium is low: You may see problems with calcium/alkalinity stability, precipitation, slower coral growth, or “drop-outs.”

• If magnesium is high: Usually less problematic, but excessive levels can upset ionic balance or waste resources.

• Trend monitoring is more valuable than isolated values: check how Mg changes over days/weeks, especially after supplementation or water changes.