Waterbox Magnesium 500mL

Waterbox Magnesium is a concentrated liquid Core Element supplement that keeps magnesium in the ideal range for a thriving reef. Magnesium is the element that lets your tank hold proper calcium and alkalinity levels, so when it drifts low, everything else becomes hard to keep stable. Dosing this supplement keeps calcium and alkalinity working together, which drives better coral growth and overall reef health. Part of the Waterbox Method lineup, made under strict lab conditions. Pair it with the rest of our reef additives and supplements.

Why Magnesium Matters

• Unlocks calcium and alkalinity: proper magnesium prevents calcium and alkalinity from precipitating out, so your other supplements actually stay in solution and available to corals.
• Drives coral growth: stable magnesium supports the skeletal growth and color of stony corals and clams.
• Corrects the hidden culprit: when calcium and alkalinity refuse to hold no matter how you dose, low magnesium is usually the reason.
• Concentrated and clean: a Waterbox Method formula produced under strict laboratory conditions from high-purity ingredients.

Dosing

• Dose rate: 5 mL raises magnesium by about 3.75 ppm in 25 gallons (100 L).
• Target range: the Waterbox Method recommends keeping magnesium at 1200 to 1400 ppm.
• How to dose: add to a high-flow area of the sump or display. Test first, then raise gradually rather than all at once, and retest after dosing.
• Test regularly: confirm your level with a magnesium test kit before and after adjusting.

Specifications

Recommended Pairings

• Red Sea Magnesium Test Kit, so you dose to a number instead of guessing
• Brightwell Reef Code A (Calcium) and Reef Code B (Alkalinity), the two elements magnesium keeps in balance
• Waterbox Magnetic Glass Cleaner, more Waterbox gear for tank upkeep
• Additives & Supplements, the full reef dosing lineup

FAQ

When should I dose magnesium?
Whenever a test shows you below the 1200 to 1400 ppm range, or when your calcium and alkalinity will not hold steady despite regular dosing. Low magnesium is the usual reason those two drift.

How much will one bottle raise my tank?
At 5 mL per 25 gallons for roughly 3.75 ppm, a 500 mL bottle covers a meaningful correction on most home reefs. Always test, raise gradually, and retest.

Is it reef safe?
Yes. It is formulated specifically for reef aquariums with corals, clams, and invertebrates.