Nyos Magnesium Reefer Test Kit | High-Precision Mg Titration for Saltwater Reef Aquariums

The Nyos Magnesium Reefer Test Kit is a precision titration kit that measures magnesium (Mg) in saltwater reef aquariums down to 15 mg/L resolution — sharp enough to spot a slow drift before calcium and alkalinity start to fall apart. Made in Germany with reagents calibrated against AAS and NIST standards, it delivers laboratory-grade accuracy at a hobbyist price. Browse our full water testing kits collection or explore other saltwater reef supplies.

Why Magnesium Matters in a Reef Tank

Magnesium is the third leg of the calcium / alkalinity / magnesium triangle. Without enough Mg, calcium carbonate precipitates out of solution and your Ca and KH crash together — even when you're dosing them. Magnesium is also a structural component of stony coral and coralline algae skeletons, so it directly drives growth, color, and skeleton density in SPS, LPS, and clams.

Most reef hobbyists target 1280–1350 mg/L (natural seawater is ~1280 mg/L), and SPS-heavy tanks running 2-part, calcium reactors, or kalkwasser often aim for 1350–1450 mg/L. Whatever your target, you can't hit it without testing — and you can't react to a drift you can't see.

Features

• ~50 tests per kit — months of weekly testing on a single tank
• 15 mg/L resolution — sharper than most hobby kits, catches slow drift early
• Range up to 1600 mg/L — covers natural seawater and elevated SPS reef levels
• Three-part titration with sharp pink-to-blue endpoint — easy to read, no guesswork
• German-made reagents calibrated against AAS and NIST standards (EN ISO 9001)
• Calibrated dropper and precision syringes for repeatable drop volume across tests
• Designed for marine water — reagents account for interfering ions in saltwater

How to Test

1. Fill the supplied test vial to the marked line with tank water using the syringe.
2. Add Reagent MG-1 per the included pictogram instructions and swirl.
3. Add the measured scoop of MG-2 powder and swirl until dissolved — the sample turns pink.
4. Titrate MG-3 drop by drop, swirling after each drop, until the color shifts from pink to clear blue.
5. Read the magnesium concentration directly from the syringe scale.

For tanks dosing 2-part, calcium reactors, or kalkwasser, test weekly. Stable, lightly stocked reef systems can usually get away with testing every 1–2 weeks — magnesium drops slowly compared to calcium and alkalinity.

Specifications

Recommended Pairings

• Red Sea Reef Foundation Pro Multi Test Kit (Ca, Alk, Mg) — round out a full reef-parameter testing setup
• Red Sea Calcium Pro Test Kit — pair Mg testing with calcium for the full picture
• Salifert KH / Alkalinity Test Kit — KH is the third leg of the triangle, test it alongside Mg and Ca
• Red Sea Reef Foundation C — Magnesium 500 mL — dose this if your Mg comes back low
• Browse all reef additives and supplements

FAQ

How often should I test magnesium?
Weekly is ideal for SPS-dominant tanks or any system actively dosing 2-part, calcium reactor effluent, or kalkwasser. Stable mixed reefs and softie tanks can usually test every 1–2 weeks. Magnesium falls slowly compared to Ca and Alk, but if it crashes, your other parameters will follow.

What's the ideal magnesium level for a reef tank?
Natural seawater sits around 1280 mg/L. Most reefers target 1280–1350 mg/L for mixed reefs, and 1350–1450 mg/L for SPS-heavy systems running elevated calcium and alkalinity. Anything below ~1200 mg/L starts to cause Ca/Alk instability.

How is this different from a Hanna or Salifert magnesium test?
The Nyos kit uses a true titration with a sharp pink-to-blue endpoint and 15 mg/L resolution — finer than most hobby titration kits, and the endpoint is easier to read than a fading color match. Reagents are German-made and calibrated against laboratory standards, so batch-to-batch consistency is excellent.

Does the kit work for freshwater?
No. The reagents are formulated for saltwater chemistry — interfering ions in marine water are accounted for. Use a freshwater-specific magnesium kit if you're testing planted-tank or African cichlid water.

How long do the reagents last?
Sealed and stored at room temperature out of direct sunlight, Nyos reagents typically remain accurate for 1–2 years. Once opened, use within ~12 months for best precision and replace if the color of MG-1 or MG-3 looks off.