Seachem Reef Calcium

Seachem Reef Calcium is a concentrated bioavailable polygluconate complex of calcium that supports the rapid uptake required by stony corals, coralline algae, and other reef invertebrates. Unlike standard calcium chloride or calcium hydroxide supplements, the polygluconate form is far less likely to be lost as a precipitate, so more of every dose reaches your coral.

Use it alongside our full additives and supplements collection, verify dose with a calcium test kit, and pair with Seachem Prime for routine water changes.

Features

• Bioavailable polygluconate complex, taken up directly by stony corals and coralline algae
• Minimal precipitation, more of each dose stays in solution
• Does not deplete strontium, magnesium, or other reef elements
• Compatible with all standard 2-part and balanced reef dosing programs
• Available in three sizes for nano up to large reef systems

Dosing

• Standard dose: 1 capful (5 mL) per 80 L (20 US gallons) once or twice per week
• Each capful raises calcium by approximately 1 mg/L per 80 L
• Target calcium for reef tanks is typically 380 to 450 mg/L
• Test weekly and adjust dose to match consumption

Specifications

Recommended Pairings

• Red Sea Calcium Pro Test Kit for weekly verification
• Salifert Calcium Test Kit as a budget option
• Seachem Prime for water changes
• Browse all reef supplements

FAQ

Will Reef Calcium replace my 2-part?
For light to moderate reef demand, yes. For SPS-dominant or high-demand reefs, use Reef Calcium alongside an alkalinity supplement to keep Ca and Alk balanced.

Does it raise alkalinity?
No, this is calcium only. Pair with an alkalinity supplement to maintain balance.

Is it safe with inverts and fish?
Yes, when used at the recommended dose Reef Calcium is safe for fish, corals, and invertebrates including clams and shrimp.