TheNT Labs Marine Lab Magnesium Test Kitis a precise titration test that measures magnesium (Mg) levels in saltwater and reef aquariums. Magnesium is one of the three pillars of reef chemistry — alongside calcium and alkalinity — and stable Mg levels (1280–1350 ppm) are essential for healthy coral growth, calcification, and resistance to nuisance algae. See more water testing kits and saltwater supplies.
Why Test for Magnesium
- Locks in Ca and Alk— without sufficient Mg (~3x the calcium concentration), calcium and alkalinity precipitate out and crash together.
- Drives coral growth— SPS, LPS, and clams need stable Mg to build skeletons and color up.
- Suppresses nuisance algae— bryopsis and other pest algae often retreat when Mg is dosed back into the ideal range.
- Reagent-based titration— visible color change makes endpoints easy to read.
How to Use
- Rinse the supplied vial with aquarium water and fill to the indicated level.
- Add the supplied reagents in the order listed in the included instructions.
- Add titrant drop by drop, swirling between drops, until the color changes from red/pink to a clear blue/green endpoint.
- Multiply the number of drops by the conversion factor on the instruction sheet to read your magnesium level in ppm.
Test weekly, or any time you change salt brand, increase calcium/alkalinity dosing, or notice slowed coral growth or unexplained algae.
Target Range
| Aquarium Type | Ideal Magnesium (ppm) |
|---|---|
| Mixed reef | 1280–1350 ppm |
| SPS-dominant reef | 1300–1400 ppm |
| Fish-only saltwater | 1250–1350 ppm |
| Natural seawater | ~1280 ppm |
Specifications
| Brand | NT Labs |
| Series | Marine Lab |
| Tests For | Magnesium (Mg) |
| Method | Drop-count titration |
| Water Type | Saltwater & Reef |
| Tests per Kit | 35 tests |
| Made In | United Kingdom |
Recommended Pairings
- Red Sea Reef Foundation C — Magnesium (500 mL) — raise Mg back to target.
- Red Sea Calcium Pro Test Kit and Salifert KH/Alkalinity Test — round out the reef chemistry trio.
- Red Sea Reef Foundation Pro Multi Test Kit (Ca, Alk, Mg) — bundle option for all three core parameters.
- IceCap Magnetic Test Kit Mixer — faster, more accurate endpoint reading.
- Browse all water testing kits | Additives & supplements
FAQ
Q: Do I need to test for magnesium if I do regular water changes?
A: Yes. Salt mixes vary in Mg content, and corals and calcifying organisms consume Mg between water changes. Testing weekly catches drift before it crashes Ca and Alk.
Q: What does it mean if my magnesium is low?
A: Low Mg (under ~1250 ppm) lets calcium and alkalinity precipitate, slows coral growth, and can encourage bryopsis algae. Dose a magnesium supplement to restore the 1280–1350 ppm range.
Q: How often should I test?
A: Weekly for active reef tanks, monthly for fish-only saltwater, and any time you switch salt brands or notice unusual coral or algae behavior.
Q: Is this for freshwater tanks?
A: No — this kit is calibrated for the high Mg concentrations found in saltwater (~1300 ppm). Freshwater Mg is typically tested as part of a GH/general hardness kit.
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