Kalkwasser has been called the king of aquarium additives. But what is it, what does it do, and why would you want to add it to you aquarium?

What Is Kalkwasser?

Kalkwasser is water mixed with powdered lime or calcium hydroxide. The kalkwasser additives aquarists purchase are made of dried powder or kalk, and this powder is mixed with purified RO/DI water. Seachem Reef Kalkwasser and Brightwell Aquatics Kalk+2 Kalkwasser Supplement are our recommended kalkwassers.

What Does Kalkwasser Do?

- Adding kalkwasser will cause the pH of your aquarium to rise because it’s a base. Keeping a proper high pH of 8.2-8.4 can help your corals grow faster and help stop the growth of unwanted algae.

- Kalkwasser raises calcium and alkalinity. Calcium and alkalinity are what corals, snails, and clams use to build their bodies. In a reef aquarium the calcium and alkalinity levels drop as the animals inside the tank grow. Using kalkwasser to ensure calcium and alkalinity are at proper levels can dramatically increase the growth of your corals and invertebrates.

- Adding kalkwasser to your aquarium removes phosphates from the aquarium water by causing it to precipitate out of solution. Phosphate can fuel unwanted algae growth or cause corals to grow brittle skeletons. Using kalkwasser can help eliminate or reduce the need for other phosphate removers such as Phosban or Phosphate RX.

How Do You Use Kalkwasser?

Kalkwasser is sold as a powder. You first must mix this powder with purified RO/DI water. You then can add it to the aquarium. It’s very important you don’t add too much at once. Kalkwasser has a very high pH of 12.3 which can raise the pH of your aquariums so fast that it can harm the fish and corals inside. To add the solution slowly there are a few methods.

Kalkwasser Reactors – Kalkwasser reactors such as the IceCap Kalk Large Mixing Reactor and the Two Little Fishies KW Reactor are the most efficient way to use kalkwasser. They can be used in conjunction with either a dosing pump or an auto top off. These reactors constantly stir kalk powder into water making sure that the water exiting the reactor has the maximum amount of kalk powder dissolved in it. Kalk reactors also reduce the maintenance associated with the other methods as kalk powder only needs to be added every few months.

Dosing Pumps – Dosing pumps include the Milwaukee MC720 Dosing Pump Kit, and the Neptune DOS. These will all pump kalkwasser very slowly into your aquarium. And in the case of the Neptune DOS and Milwaukee Dosing Pump Kit, the pump will shut off if the aquarium pH ever rises too quickly.

ATO Reservoirs – If you have an auto top off such as the IceCap ATO EZ System or SpectraPure Liquid Level Controller you can add kalk powder to the reservoir of top off water your ATO draws from. This will ensure that only a small amount of kalkwasser is added at a time.

Manual Drip – The simplest way to dose kalkwasser is to slowly drip the solution into your aquarium. This is usually done with airline tubing and a ball valve. We do not recommend this approach because if the drip rate is too fast your aquariums pH may rise too quickly and harm the animals in your aquarium. Additionally, a new solution of kalkwasser needs to be mixed up every day which can be labor intensive.

Alternatives to Kalkwasser

If this all seems like too much work an alternative to kalkwasser is the two part method which utilizes two separate solutions: one with calcium and one with alkalinity, such as ESV B Ionic. These chemicals can simply be poured into the aquarium without a risk of raising the pH too high. However, two part additives will not give you the elevated pH that properly dosed kalkwasser will. It will also not precipitate phosphate, and it will be significantly more expensive in the long run.