kalkwasser reactor examples

Corals need the right balance of calcium and alkalinity (bicarbonate) to build new skeleton and tissue. If there is an imbalance of either calcium or alkalinity it can inhibit coral growth and make it harder to maintain pH. The goal is to keep calcium at 380-450 ppm and alkalinity at 7-11 dK.  While you can test and add calcium and alkalinity supplements separately, it requires careful dosing and retesting to keep the levels in balance. Many reef aquarists like kalkwasser because it adds both calcium and alkalinity at the same time and at the right ratio.

"Kalkwasser" is German for limewater. Kalkwasser is made by dissolving calcium hydroxide Ca(OH)2 in fresh RO/DI water. The solution is then slowly dosed into saltwater to add calcium, increase carbonates, and boost pH. 

Dosing Kalkwasser Manually

Manual dosing

It takes some effort to mix up the kalkwasser solution and then manually add it to your reef. Some aquarists use kalkwasser in their ATO systems for topping off the tank which does automate the additions but makes it hard to meter the doses. Alternatively, you can use a dosing pump to pull the kalkwasser solution on a schedule and add it to your tank slowly which is great, but still requires the weekly mixing and filling of a new kalkwasser solution.  Enter a Kalkwasser Reactor which is the most automated approach to using Kalkwasser because you get the control of using a programmable dosing pump but also alleviate the need for weekly mixing of kalkwasser solution.  The reactor does that for you! 

What is a Kalkwasser Reactor?

A kalkwasser reactor or Kalkwasser Stirrer is a sealed chamber where freshwater and calcium hydroxide powder are mixed together. A programmable pump or small powerhead on a timer feeds freshwater into the reactor which then pushes the already mixed Kalkwasser solution into your aquarium via the outlet of the reactor. We recommend this feed pump be independent of your ATO system for the sake of precision dosing but in many cases your ATO pump can be used.  Since the Kalkwasser is mixed with fresh water, you are technically topping off our tank with every dose.  

Sometimes the reactor has a separate re-circulation pump that periodically stirs the kalkwasser solution for you, others rely on using the power of the feed pump alone to mix the solution, the Ice Cap Kalkwasser Reactor pictured in our diagram uses a magnetic stirrer. The exact design may vary depending on the exact model you have which means the setup can vary too but the benefits are all the same.  

You can fill the reactor with an abundance of calcium hydroxide powder, the kalkwasser solution will always stay at maximum concentration and it only requires a monthly-bimonthly cleaning and refill. The use of a metered dosing pump or even your ATO pump means the additions will be automated and controlled, alleviating the need for manual additions. 

How to Set Up a Kalkwasser Reactor

Kalkwasser Reactor Diagram

Required Equipment:

  • Kalkwasser Reactor
  • Calcium Hydroxide Powder (Kalkwasser)
  • Freshwater Reservoir with RO/DI water
  • Dosing Pump or feed pump - Alternatively, you can use your ATO system.

The image above shows how the Kalkwasser system is set up using a programmable dosing pump.  When using your ATO, the programmable pump is simply the pump attached to your ATO system. There are a few different reactor designs on the market which may be set up a little differently so always defer to the manufacturer's instructions. 

When used with a programmable dosing pump (preferred), you want very small, frequent doses. A slow drip (+/- 1 drop every 5-10 seconds) can be effective but it all just depends on your tank's demand for calcium and alkalinity. 

When used with an ATO, your doses will be administered when the top-off pump is initiated and will dose as much as it takes to return the water level. While this is an easy setup, it also means you don't really have any control over the frequency and quantity of each dose. pH spikes can also be problematic in this scenario which is why it's not the best long-term solution.    

In either case, your particular tank's demand for calcium and alkalinity will ultimately dictate your dosage. Once set up, it's best to start very conservatively and adjust the dosage accordingly to maintain stability in your aquarium. Always monitor pH levels very closely when using Kalkwasser because it does spike your pH, which is why you must make very small, incremental doses.  If you dose too much, too quickly, you run the risk of a dangerous pH spike. An active pH monitor is convenient for this situation.  

Benefits of Using a Kalkwasser Reactor

  • It's the easiest approach to major element stability in a reef tank. Trace elements and magnesium should be maintained separately. 
  • The reactor automatically keeps the solution at maximum saturation. You won’t have to worry about the kalkwasser losing strength and throwing off the calcium to alkalinity ratio.
  • Kalkwasser solution is automatically dosed in small amounts. This prevents pH spikes and keeps the water chemistry stable.
  • You won’t have to use a slow gravity drip or stand at the aquarium carefully pouring kalkwasser solution into the tank.
  • Maintains both calcium and alkalinity in a reef aquarium at the proper ratio.
  • You get a boost to your pH which is often depressed because of too much-dissolved CO2 which creates carbonic acid. 
  • Dosing Kalkwasser during daylight hours can help reduce the severity of the natural pH swing. 

Learn More: 10 Frequently Asked Questions about Kalkwasser