Avast Marine

K2 Kalk Stirrer

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Discontinued by Bulk Reef Supply
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Once you get a kalkwasser stirrer you will never go without one again!

Avast Marine has been producing acrylic based aquarium equipment for years, using high-quality components. The K2 Kalk Stirrer is a dedicated reactor for dosing kalkwasser into reef tanks, in a safe and controlled matter. Instead of using a large reservoir of lime water, a kalkwasser stirrer can be connected directly to any freshwater reservoir, or even RODI unit saving you mixing time, and space. 

The K2 Stirrer is designed to stir the kalk slurry 24/7, and does not require any additional mixing pumps or timers. Constant mixing allows the K2 to always have a steady concentration of kalkwasser solution available for your reef, aiding in keeping your calcium and alkalinity levels steady. Some reactors require on a pressurized chamber where the Avast reactors do not. They rely on gravity draining, which is much safer and reliable. Pressurized reactors are prone to leaks which can easily damage and stain floors, which makes the K2 Stirrer a no-brainer. 


Avast Marine Kalk Stirrers will continuously mix kalkwasser 24 hours a day. That will ensure the freshest and most potent kalkwasser solution is being dosed into your reef tank at any time.



  • Recommended for tanks up to 800 gallons
  • 1/4" Push Connect Input
  • 1/2" Barbed Output
  • Non-pressurized chamber
  • Saves space & time
  • Top load design
  • Simple & safe


What is Kalkwasser?

Kalkwasser (Kalk) is calcium hydroxide and when mixed with freshwater becomes a magical solution that can add calcium and alkalinity to your reef aquarium in balanced proportions. Calcium hydroxide is commonly used in top-off reservoirs or in a kalkwasser reactor and then slowly added to the tank multiple times a day. As kalkwasser is added it will help replenish calcium and alkalinity that your corals will consume but also slightly increase your pH for a short time. Due to the pH increasing effect, care does need to be taken that the solution does not get overdosed and that your pH is not increasing more than 0.20 pH per dose. 


What do I need to use the K2 Kalk Stirrer?

You will need a couple additional accessories with the K2 Kalk Stirrer, one of which is a feed pump. In most cases, a peristaltic pump will be the best solution for the benefit that they are very accurate and also have anti-siphon characteristics, but inexpensive pumps like an Aqualifter can work just fine, but care does need to be taken that it does not back-siphon. It is much safer to feed a kalkwasser reactor from a reservoir that contains RODI water, than a direct connection to a RODI system. In most cases, the refilling of the reservoir can be automated and more efficient. The drain barb uses 1/2" flexible tubing and will allow the reactor to drain into a high-flow area of your sump. We have found the Black Vinyl Tubing to look very nice with the Avast Marine reactor. 

Another requirement is kalkwasser itself, and you can choose your favorite brand of kalkwasser. We suggest using BRS Bulk Kalkwasser and if you need to adjust your levels you may want to get the BRS Kalkwasser Starter Package which includes calcium, alkalinity, and magnesium supplements too.  


How much Kalkwasser do I use?

The amount of kalkwasser reactor used will vary from aquarium to aquarium and will depend on the amount of water your tank evaporates per day, and also the demand for calcium and alkalinity. Please refer to the chart at the bottom of the page for starting recommendations. 



Once every two weeks, the kalkwasser solution in the K2 will need to be replenished, but only rinsed out once a month to make room for new kalkwasser. Since kalkwasser can help purify the freshwater that is fed into the reactor, the precipitate can form at the bottom that will be removed when the reactor is rinsed out. Rinsing the reactor only takes a few minutes and with the included union barb and push connect fitting, it is very simple too. It is also suggested that once every 6 months the reactor is cleaned with vinegar to help remove any calcium build up or deposits. 



  • Max Tank Rating - 800 gallons
  • Dimensions - 7" L x 7" W x 21" H
  • Input Tube Size - 1/4" Push Connect
  • Output Tube Size - 1/2" Barb
  • Output Capacity - 14 Gallons per Day 
  • Power Consumption - 3W @ 120VAC

PDF Owners Manual Owners Manual


What's Included?

  • 1x K2 Kalkwasser Stirrer Body
  • 1x K2 Kalkwasser Stirrer Lid & Motor
  • 6 ft 1/4" Push Connect Tubing


Kalkwasser Calculator:

You will need to determine your aquariums evaporation amount on a daily, weekly, or biweekly basis, and then follow the chart below for starting recommendations with the Avast Marine K2 Kalkwasser Reactor.

Gallons/Day Gallons/Week Gallons/Biweekly Cups of Kalk Biweekly
0.25 1.75 3.5 0.25
0.5 3.5 7 0.5
0.75 5.25 10.5 0.5
1 7 14 0.75
1.25 8.75 17.5 1
1.5 10.5 21 1.25
1.75 12.25 24.5 1.5
2 14 28 1.75
2.25 15.75 31.5 2
2.5 17.5 35 2
2.75 19.25 38.5 2.25
3 21 42 2.5
3.25 22.75 45.5 2.75
3.5 24.5 49 3

If your aquarium evaporates more than 25 gallons per week, it is highly suggested to refill the reactor once a week. 

Gallons/Day Gallons/Week Cups of Kalk Weekly
3.75 26.25 1.5 
4 28 1.5 
4.25 29.75 1.75 
4.5 31.5 1.75 
4.75 33.25
5 35
5.25 36.75 2.25 
5.5 38.5 2.25 
5.75 40.25 2.5
More Information
UPC 713783681563
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Product Questions

What is the height of the output?
Question by: Zach on Feb 27, 2019, 12:41 AM
Thanks for contacting BRS!
The height of the output is 16". Have a great day!
Answer by: Noah on Mar 15, 2019, 9:51 AM