I am a kalkwasser fan. I find that it is a great option for controlling both alkalinity and to inflate pH levels. When I first began using kalkwasser, I simply put it in my ATO container and stirred it up. Part of this method results in a lot of sediment left behind. I very quickly wearied of cleaning this out weekly and began researching kalkwasser stirrers. If your reefing goals include reducing the amount of time you spend maintaining your tank while maximizing the time you spend enjoying the tank, I highly recommend a kalk stirrer.

What is a kalk stirrer?

All brands of kalk stirrers I researched work by supplying a chamber with rodi water. This chamber has an excess of undissolved kalkwasser. The mixture is stirred continuously or intermittently. The result is a fully saturated kalkwasser solution that can be dosed to the tank. As the solution is dosed to the tank, new rodi water is supplied to the chamber. Maintenance includes 2 main things: 1) resupplying the chamber with a kalkwasser powder as needed to ensure a fully saturated solution and 2) monthly chamber cleanings to remove residue build up.

Reason 1 and 2

I considered several brands of kalk stirrers, but ultimately choose the Avast Marine K1 Kalk stirrer. This kalk stirrer is rated for up to 400 gallons. My tank is 175 gallons, so this is well within those limits. The second reason I opted for the Avast Marine kalk stirrer is the built in probe holder. This allows monitoring of either conductivity or ph. Once the values drop, your controller can be set to alert you to add more kalkwasser to the chamber.

Brandi's Avast Marine Kalk Stirrer

My kalk stirrer under my tank.

Reason 3

Bernoulli’s Principle

Next, the output port is large. It may look unsightly, but is very important due to a little fluid dynamics law known as Bernoulli’s principle. Bernoulli uncovered that there is a constant relationship between


  1. the total mechanical energy of a moving fluid,
  2. the gravitational potential energy of elevation,
  3. the energy of fluid pressure, and
  4. the kinetic energy of the fluid motion.

The infamous mathematician Euler was able to distill these relationships into the following equation:

Bernoulli's Equation

Bernoulli’s Equation. P is pressure, rho is density, v is velocity, h is height and g is the acceleration due to gravity (9.81m/s^2)

And voila! This is the mathematical magic for why planes fly, vacuum cleaners suck, shower curtains float in on you while showering, and part of the reason you need a large port for your kalk stirrer. It is counterintuitive (as are most conservation of energy laws), but as the liquid spins inside the kalkwasser stirrer, it creates a negative pressure/vaccum/sucking force. This negative pressure sucks the liquid in the output tube back up into the stirrer. I know you’re thinking, “But Brandi, conservation of energy laws would indicate that this pressure disappears when the liquid is no longer moving.” Normally you would be correct, but we have another law of nature to deal with – the polarity of water.

Cohesion and Adhesion

Water is a polar molecule, which means each molecule is like a tiny magnet. It not only sticks to itself (cohesion), but it sticks to other objects (adhesion). Smaller tubing allows water tension to form and essentially plugs the chamber resulting in a buildup of negative pressure in the chamber. Larger tubing negates the cohesive and adhesive properties of water – allowing the pressure to come to equilibrium inside and outside of the chamber. When you take into account kalkwasser’s tendency to leave build up behind, smaller tubes are begging for clogs and overflows.

Reason 4

I am sure everyone reading this maintains their equipment at regular time intervals. I’ll tell you a secret: I often let my maintenance routines go much longer than I should. Shhh! Don’t tell anyone. If the kalkwasser is allowed to build up in a large tube, you’ll eventually be left with a small opening, clogs, and overflows. This brings me to the final reason I like the Avast Marine Kalk Stirrer. The motor is on top of the water chamber. In the event that the chamber does overflow, the water should not get on any electrical parts which of course would lead to death and destruction. I am being a bit hyperbolic, but we all know that water and electricity is bad. If this can be avoided with an elevated motor, I think that is a worthwhile feature.

Let me know which kalk stirrers you’ve tried and what you like and dislike about them.

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