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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 your aquarium?
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.
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 unwanted algae growth.
Kalkwasser raises calcium and alkalinity. Corals, snails, and clams use calcium and alkalinity 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 phosphate 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.
Kalkwasser is sold as a powder. First, mix the powder with purified RO/DI water. Then add it to the aquarium. You mustn’t add too much at once. Kalkwasser has a very high pH of 12.3, which can raise your aquarium's pH so fast that it can harm the fish and corals inside. To add the solution slowly, you can use a few methods.
Kalkwasser ReactorsKalkwasser reactors such as the IceCap Kalk Large Mixing Reactor and the Two Little Fishies KW Reactor are the most efficient way to use kalkwasser. You can use them with either a dosing pump or an auto top-off. These reactors constantly stir kalk powder into the water, ensuring the water exiting the reactor has the maximum amount of kalk powder dissolved in it. Kalk reactors also reduce maintenance associated with other methods, as kalk powder only needs to be added every few months.
Dosing PumpsDosing pumps include the Milwaukee MC720 Dosing Pump Kit, and the CoralVue Hydros Sole Dosing Pump. These will all pump kalkwasser very slowly into your aquarium. With the Neptune DOS and Milwaukee Dosing Pump Kit, the pump will shut off if the aquarium pH rises too quickly.
ATO ReservoirsIf you have an auto top off such as the IceCap ATO EZ System or JBJ Nano ATO Advanced Auto-Top-Off System you can add kalk powder to the reservoir of top off water your ATO draws from. This ensures only a small amount of kalkwasser is added at a time.
Manual DripThe simplest way to dose kalkwasser is to drip the solution slowly 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 aquarium's pH may rise too quickly and harm the animals in your aquarium. Additionally, you need to mix a new solution of kalkwasser every day, which can be labor-intensive.
If this all seems like too much work, an alternative to kalkwasser is the two-part method, which uses two separate solutions: one with calcium and one with alkalinity, such as Two Little Fishies C-Balance. You can pour these chemicals into the aquarium without risking a pH spike. However, two-part additives will not give you the elevated pH that properly dosed kalkwasser will. They also won't precipitate phosphate, and they will be significantly more expensive in the long run.
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