How to use the Kalkulator

If you are setting up a stirrer for the first time or have had trouble maintaining a consistent result from kalkwasser dosing please follow the directions below:

  1. Determine your average daily evaporation level and enter it into the calculator.  This does not need to be 100% perfect but it should be based on actually measuring for at least a few days to a week.
  2. Enter the % of that evaporation that you would like to make up with kalkwasser.  There are some helpful examples down the page if you need some guidance with this.
  3. Based on this, you will get a kalkulation for how much kalkwasser should be dosed per day and how much dry kalk should be added to the stirrer to deliver saturated kalkwasser for a period of 14 or 30 days.  
  4. Minimum fill amount for K1 is 1/2 cup and for K2 is 1 cup, if you get a fill kalkulation less than that, use this as your starting amount instead of the kalkulation. 

Kalkulating a fixed dose

If you already dose a fixed amount of kalkwasser per day and are happy with the results you can still use the Kalkulator to determine the correct fill level for a 14 or 30 day supply by doing the following.

  1. Set make up % to 100%
  2. In the daily evaporation field, simply enter the daily dose of kalkwasser
  3. Based on this, you will get the proper amount of dry kalk to add to the stirrer for a consistent saturation level for a period of 14 or 30 days 

Monitoring and pH output

The following chart is based on actual measurements using all the most popular brands in our stirrer:  

When performing the same test except using a kalk addition every 30 days, you can expect the following results, again based on actual measurements in our stirrer: 

As you can see, pH is far more stable when kalk powder is measured carefully and added every 2 weeks.  That said, the convenience of 30 day additions cannot be ignored so if you choose this method, use Mississippi Lime.  PH of Mississippi Lime Vitacal is still 11.75 at day 24 so there is absolutely a benefit to the tank with this method, it is just not as consistent in our bench tests.  

About these test and home testing:

All of our tests were performed using lab grade pH testing equipment and following standard lab procedures.   We use an Apera Instruments PH8500-HT pH meter along with Swiss Labsen 861 pH electrode with weekly 3pt calibration, designed specifically to measure caustic solutions in the pH range of 11-14. 

We also tested many samples with an Hanna pHep 0.1 resolution pocket tester and while the accuracy was not good enough for our research, we have concluded that it is valuable as a guide.  Meaning, we noted that as the pH dropped over time at roughly the same rate as was measured by the more expensive equipment, it gave an indication of the potency rather than an absolute. We feel this inexpensive meter will no doubt outperform either a probe that is left to sit in the stirrer as a monitoring device or a pH probe that is used to monitor aquarium water to spot test a sample should you want to perform some of these tests for yourself and we offer them here.


Q: What size stirrer should I buy?

A: K1 can deliver 2.5 gallons of saturated kalkwasser per day.  K2 can deliver 5 gallons per day.  So while we do offer a "tank rating" based on our experience, daily kalkwasser usage is the ultimate deciding factor for this.

Q: Why is there a pH probe holder on my stirrer if you do not suggest monitoring pH inside the stirrer?

A: 12 years ago when we produced 40-50 kalk stirrers a year, someone asked us to include this feature, we didn’t see the harm and included it as a revision.  We had no idea at the time the thousands of stirrers we would sell in the following years and that it would somehow become controversial LOL.  We are in the process of changing tooling to remove this port from future stirrers since we have found samples pulled directly from the output measured with a pH meter produce the most reliable readings.

Q: Should I run the stirrer intermittently to prolong the motor life?

A: No!  We want the kalk to be moving at all times, if it is allowed to settle for too long it can clump or solidify in the bottom of the stirrer causing additional torque on the motor at startup, this will reduce motor life much more quickly than running 24/7.

Q: How long does the motor last?  Is it replaceable?

A: 3 years is typical life when run 24/7.  The motor is easily replaced and takes about 10 minutes to do. 

Q: Do you have any plans for a slurry reactor or can I modify my stirrer to dose a kalk slurry?

A: Absolutely not.  We encourage experimentation but there is overwhelming evidence that this is borderline reckless.  We find that most people who have asked this question are very far from the recommendations of the Kalkulator and when introduced to the proper fill rates with a make up % of 50% or more are instantly more successful managing tank pH and have no need for a solution more than 10,000x more base than seawater. 

Q: What % of make up should I start with?

A: Generally speaking, 25% would be the lowest we would recommend as a starting point.  Consumption of calcium and alkalinity by the organisms, environmental co2 (carbonic acid), seasonal variations, starting water pH, these are all variables that will be unique to your tank. Monitor your levels and make adjustments as needed, slowly bringing this % up over time until your tank finds a balance.  Keep in mind that as the system pH increases, corals are more easily able to absorb calcium (just like our human bones), which in turn accelerates growth, which keeps increasing demand.  This is a FEATURE of kalkwasser dosing so you may find you have to keep adding more and more until you reach 90-100% make up for SPS dominated reefs. 

Q: Can I use BRS Pharma Kalk?

A: Pharma is a very high quality kalk, but unfortunately it does not work in our stirrers.  It has a density 1.7x of normal calcium hydroxide and has a tendency to clump and turn to a solid, which in turn burns out stirrer motors. We are exploring options to utilize this kalk in the future.

Q: What about other brands of kalk?

A: We have tested most commonly available brands of kalk, there is a reason we made the investment to bring back what we feel is the best available calcium hydroxide for stirrer use.  If you have questions about a specific product, please contact us and we are happy to discuss.