Kalkwasser Dosing Calculator

How much it adds

The limit is how much water you top up. Kalk can only go in with the water that replaces evaporation, so a tank that evaporates little can’t take much kalk.

From 41 meq/L alkalinity and 816 mg/L calcium at 25 °C. Seachem’s figure for its own product is close: 4 L of saturated solution raises 150 L by 24 mg/L of calcium.

Mixing it

Bulk Reef Supply says a solution holds at most about 2 teaspoons of powder per US gallon; Seachem gives 6 g per 4 L for a saturated solution. Bulk Reef Supply’s own dosing guide suggests ½–1½ teaspoons per gallon depending on demand. Let it settle for 30 minutes, and keep the reservoir’s intake off the bottom so the sediment stays behind.

Stir it as little as possible and keep the reservoir covered. Bulk Reef Supply says air lets carbon dioxide in, which weakens it.

Safety

Kalk raises pH. Bulk Reef Supply says keep rises within 0.2, and that pH above about 8.4 means you’re dosing too fast. Too much at once can spike pH dangerously or cause precipitation, so start weak and test daily for the first few days.

The powder is caustic. Seachem’s label warns it causes burns: wear gloves and eye protection and avoid breathing the dust. Never add the powder straight to the tank.

Night dosing

Bulk Reef Supply notes that dosing kalk at night can offset the overnight pH drop. See reef tank pH.

Can kalk cover all my alkalinity demand?

Only if your evaporation is high enough. The calculator shows how much it covers.

Can I put kalk in my ATO?

Yes, with care. Bulk Reef Supply describes dosing it through top-off, starting weak and testing daily.

Is kalkwasser dangerous?

The powder is caustic and a sudden overdose can spike pH. Handle and dose it carefully.