Kalkwasser — why, what it's for, and how to dose it
Kalkwasser is the manufacturer's answer to low pH, and it only does its job when it's mixed and dripped exactly the way the manufacturer says. Bio-Kalkwasser™ raises pH, adds calcium and converts excess carbon dioxide into calcium carbonate, and it's dosed at night. This covers what it is, who it's for and who it isn't, how to mix and dose it, and how it sits next to Aragonite A™, B™ and C™.
What Kalkwasser Is and What Bio-Kalkwasser™ Adds
The manufacturer's Aqua Care Guide™ explains kalkwasser in one line: it raises pH by converting carbon dioxide into calcium carbonate, which can help keep pH and alkalinity stable.
Bio-Kalkwasser is the manufacturer's version, in Step 3 – Aragonite Enhancers™. It's calcium hydroxide plus a proprietary energy blend. The manufacturer describes it as supplying hydroxide, calcium and non-nitrogenous, bioavailable energy, to help raise pH, improve pH stability and alkalinity, and build strong aragonite.
The night is where it earns its place. When the lights go off, photosynthesis stops, carbon dioxide builds up and forms carbonic acid, and pH can drop. The manufacturer calls Bio-Kalkwasser a particularly effective way to reduce that natural nightly drop.
When to Recommend Kalkwasser and When Not To
Name the limit first: it's optional. Our Step 3 page calls Bio-Kalkwasser an optional pH-and-calcium booster on top of Aragonite A, B and C, and the product page is plain that it doesn't replace them. A customer who wants one product instead of their calcium routine is asking for something it isn't.
The customer it fits has pH that runs low or drops overnight. For a low-pH reef aquarium, the Guide recommends two things together: fresh oxygenated air, and kalkwasser as part of the maintenance routine.
The product's own targets are calcium 405–440 ppm and pH 8.1–8.5. It's listed for FOWLR, LPS, Mixed, NPS and SPS aquariums, so a fish-only customer isn't ruled out.
It suits a customer who tests. Our product page notes that pH, alkalinity and calcium move together with Bio-Kalkwasser, and the manufacturer recommends monitoring all three while it's in use.
How to Mix and Dose Kalkwasser
This isn't a straight liquid dose. It's a powder that becomes a drip solution, and the order matters:
- Measure the powder by stocking level: 1 g · 2 g · 3 g per 4 L (~1 gal) of RODI water per 100 L (26 gal) of aquarium, for Lightly · Moderately · Heavily stocked.
- Mix it thoroughly to dissolve. Keep air contact to a minimum, which cuts down the undissolved particles that form.
- Let only the supernatant, the clear solution on top, enter the aquarium. The white undissolved material stays out.
- Drip it in through a drip system or a kalkwasser reactor, dosed at night.
For bigger systems, the Guide scales the same bands up: 10 g · 20 g · 30 g per 40 L (~10 gal) per 1,000 L (264 gal).
The three mixes deliver 6 · 12 · 18 ppm of calcium per 100 L (26 gal). That last number is the ceiling: the manufacturer doesn't recommend more than 18 ppm from this product per night, in conjunction with existing calcium dosing.
Q Tip Run the ceiling math with the customer before they leave. The heavily stocked mix already delivers 18 ppm per 100 L (26 gal), so there's no room for "a little extra" on top of it.
The free Quantum Aqua dosing app works out the amount for the customer's tank size and stocking level.
How Kalkwasser Fits With Aragonite A™, B™ and C™
Aragonite A™ Calcium, Aragonite B™ Alkalinity and Aragonite C™ Magnesium stay at their daily dose. Bio-Kalkwasser goes on top as the nighttime calcium and pH booster.
Aragonite A, B and C run the daily routine; Bio-Kalkwasser covers the night.
Both Bio-Kalkwasser and Aragonite A add calcium, and both work to the same 405–440 ppm calcium range. That's why the manufacturer's nightly ceiling is counted alongside the calcium the customer already doses.
The mistake to catch is the whole jug going in, sediment and all. The manufacturer is plain about it: only the clear supernatant goes in, never the white undissolved material.
The second mistake is dropping Aragonite A because kalkwasser "has calcium in it." It's a complement to the CAM routine, not a substitute for it.
What to Say at the Counter About Kalkwasser
Read aloud, something like this:
"Kalkwasser is for pH that runs low or drops at night. You mix the powder with RODI water and drip in only the clear layer on top, overnight. Keep your A, B and C going as normal, and test pH, alkalinity and calcium while you use it."
"Can I stir it up and dose the whole jug, cloudy part and all?"
"No. Only the clear solution on top goes in. The manufacturer says to keep the white undissolved material out of the tank, and mixing with as little air contact as you can means less of it forms."
"If it adds calcium, can I stop my Aragonite A?"
"No. It's a nighttime booster on top of your A, B and C, not a replacement. And because it adds calcium too, the manufacturer caps it at 18 ppm of calcium a night, together with the calcium you already dose."
"How much do I mix for my tank?"
"It goes by how stocked your tank is: 1, 2 or 3 grams in about a gallon of RODI water for every 26 gallons of tank. The free Quantum Aqua dosing app works out the exact amount for your tank."
Send them home with the free Reef Essential® Aqua Care Guide™. For the CAM targets by reef type and the A, B and C dose bands, see Talking Points: Step 3 Aragonite Enhancers™.
Frequently Asked Questions
What equipment do you need to dose kalkwasser?
The Aqua Care Guide names two ways to get it into the aquarium: a drip system or a kalkwasser reactor. Either way, only the clear supernatant goes in.
Does kalkwasser raise alkalinity in a reef tank?
The manufacturer says Bio-Kalkwasser helps improve pH stability and alkalinity, and recommends monitoring alkalinity, pH and calcium while using it. For raising alkalinity itself, the Step 3 product is Aragonite B, which the Guide calls a full-spectrum buffer.
What sizes does Bio-Kalkwasser come in, and how far does each go?
It comes in 550 g, 1.1 kg and 2.2 kg. The manufacturer lists the most each size makes as 2,200 L (581 gal), 4,400 L (1,162 gal) and 8,800 L (2,325 gal), which matches mixing at the lightly stocked rate of 1 g per 4 L (~1 gal).