Seachem Laboratories Reef Advantage Magnesium Supplement is a dry, highly concentrated magnesium blend (80,000 ppm) designed specifically for reef aquariums. This 10.6 oz container delivers powerful correction of low magnesium levels while preserving the delicate ionic balance that corals and invertebrates depend on.

Why your reef needs Reef Advantage Magnesium

• Restores depleted magnesium – Helps bring magnesium back into the optimal range so your system can maintain stable calcium and alkalinity.
• Supports coral growth and coloration – Adequate magnesium allows corals to efficiently use calcium for strong skeletons and vibrant structure.
• Helps stabilize pH – Severely low magnesium (below 800 mg/L) can lead to depressed pH and ongoing instability; this supplement helps correct that imbalance.
• Ideal for kalkwasser users – Magnesium depletion is commonly associated with kalkwasser dosing; this formula is tailored to replenish what your system loses.

Clean, reef-safe formulation

• Ammonia-free – Contains no ammonia, a common contaminant in many liquid magnesium supplements, for added safety in sensitive reef systems.
• Optimized salt blend – A precise mix of magnesium, chloride, and sulfate salts helps maintain ionic ratios similar to natural seawater.
• Minimal impact on alkalinity – When used as directed, it restores magnesium without unnecessarily disrupting carbonate hardness.

Usage guidance

• Do not overdose – Excess magnesium may enhance the loss of carbonate alkalinity; always follow manufacturer dosing directions and test regularly.
• Separate from carbonate supplements – Do not mix directly with any carbonate additive. Dose magnesium and carbonate products on alternate days or at least 30 minutes apart.
• Normal clumping – Slight clumping may occur in the container but does not affect performance; any clumps break apart easily during use.

Ingredients

• Magnesium sulfate
• Sodium chloride

Quantity: 1 container (10.6 oz)

Choose Seachem Reef Advantage Magnesium to safely correct low magnesium, support stable calcium and pH, and keep your reef aquarium thriving.

Additional information