- Sku: 393
- Vendor: Seachem
Seachem Reef Kalkwasser
Seachem Reef Kalkwasser is pure calcium hydroxide for mixing limewater, the classic way to hold calcium and pH steady in a reef aquarium. Dosed through your top-off water, it replenishes the calcium your corals pull from the water while gently lifting pH, all without clouding the tank or spiking alkalinity. It is a budget-friendly cornerstone of our reef additives and supplements.
How Kalkwasser Works
Mixed into fresh RO or DI water, calcium hydroxide forms a saturated limewater solution. As that solution drips into your reef, it delivers calcium and hydroxide ions that combine with dissolved CO2 to raise pH and replenish the calcium and carbonate corals need to build their skeletons. Because it rides in on your evaporation top-off, it doses continuously and quietly, day and night.
Why Reefkeepers Use It
- Maintains calcium at natural seawater levels for steady coral and coralline growth.
- Raises and stabilizes pH without adding to carbonate alkalinity, ideal for CO2-heavy tanks.
- Precipitates phosphate, helping keep nuisance algae in check as a side benefit.
- Pennies per dose, a jar lasts a long time compared to two-part and liquid calcium.
- Automation friendly, pairs perfectly with a dosing pump or auto top-off reservoir.
How to Use
Add 3 g (about 1 teaspoon) of Kalkwasser per 4 L (1 US gallon) of fresh RO or DI water and stir to dissolve; use up to 6 g per gallon for a fully saturated solution. Let it settle, then drip the clear limewater into a high-flow area of the sump or display through your top-off, ideally overnight. Start slowly and monitor pH, adjusting the drip rate to keep pH between 8.3 and 8.4. Never add the dry powder or unsettled slurry directly to the tank.
Choose Your Size
| Size | Makes (approx.) | Best For |
|---|---|---|
| 250 g (8.8 oz) | Up to ~80 gal of kalkwasser | Nano and small reef tanks |
| 500 g (1.1 lb) | Up to ~165 gal of kalkwasser | Larger reefs and regular dosers |
Specifications
| Brand | Seachem |
| Composition | Pure calcium hydroxide (kalkwasser) |
| Water Type | Saltwater and reef aquariums only |
| Supports | Calcium, pH, coral and coralline growth |
| Mix Rate | 3 g per gallon (up to 6 g saturated) |
| Target pH | 8.3 to 8.4 |
| Available Sizes | 250 g, 500 g |
Recommended Pairings
- Seachem Reef Trace replenishes the trace elements corals consume alongside calcium.
- Seachem Reef Strontium supports strontium levels for stony coral and coralline algae.
- Seachem Reef Plus is a broad vitamin and amino acid supplement for a thriving reef.
- Browse our saltwater and reef care for the rest of your dosing routine.
Frequently Asked Questions
Do I dose this straight into the tank?
No. Always dissolve it in fresh water and drip the clear limewater in through your top-off. Adding the powder directly can spike pH and harm livestock.
What water should I mix it with?
Use fresh RO or DI water, not saltwater. The kalkwasser goes into your evaporation top-off reservoir, which is fresh.
How is it different from two-part dosing?
Kalkwasser is far cheaper and also lifts pH, but it delivers calcium and alkalinity together at a fixed ratio. Heavy-demand reefs often run kalkwasser plus a supplement for fine tuning.
Is it reef safe?
Yes, when dosed correctly by the drip method. This product is for saltwater reef systems only, not freshwater.
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Seachem Reef Kalkwasser
