Calcium and the Saltwater Aquarium
Maintaining Appropriate Calcium Levels in a Reef Tank
Calcium is essential for many reef species, and there are three commonly available techniques to replace and maintain calcium in a reef aquarium.
It is essential to keep calcium levels high in a reef or invertebrate aquarium. The concentration of calcium in seawater is around 420 parts per million (ppm), and you should keep your marine aquarium between 420 and 500 ppm if you have calcium dependent corals or invertebrates. The reason calcium levels need to be this high is because many reef inhabitants (e.g. stony corals) need calcium in order to build their skeletons.
Synthetic salt mixes, when mixed properly, will usually yield a sufficient amount of calcium, but, over time, that calcium is consumed by calcium-hungry organisms. There are three common ways to replace calcium in a marine aquarium:
- Use of Kalkwasser (calcareous water)
- Use of a calcium reactor
- Use of a two-part additive (calcium and buffer)
Calcium Reactor
The best way to maintain calcium levels is through the use of a calcium reactor. In general terms, calcareous gravel is placed in the reactor chamber and aquarium water is then pumped through this calcareous gravel. CO2 is injected into the reactor chamber, lowering the pH to around 6.5. This makes the water in the reactor highly acidic and capable of dissolving the calcareous gravel. The result is a calcium and bicarbonate effluent which is then automatically dosed back into the system.
Kalkwasser
The next best way to maintain calcium is through the addition of Kalkwasser. Kalkwasser is a solution of calcium hydroxide or calcium oxide that is not terribly difficult to add to your system by way of a simple drip system. To make Kalkwasser, simply buy one of the commonly available commercial brands and follow the instructions carefully. Kalkwasser is fairly unstable and very caustic (a pH of over 12), and as such there are generally more risks associated with using Kalkwasser than with using a calcium reactor.
Two-Part Additive
Finally, a two part additive can be used to bring low calcium levels up, but it’s harder to maintain calcium levels using an additive. The calcium additive probably contains calcium chloride and is quite capable of quickly raising calcium levels in the aquarium. Unfortunately, the use of many calcium additives makes it difficult to maintain alkalinity levels, and, therefore, you also need part two—a buffer—to bring the alkalinity back up. In addition, these additives are generally expensive and many two part solutions actually increase non-desirable algae growth.
Conclusion
Many aquarists prefer using a calcium reactor or Kalkwasser over the long-term to maintain appropriate calcium levels in the marine aquarium. Even if they use a calcium additive to bring the calcium levels up into the 420-500 ppm range, most aquarists then prefer to maintain that calcium level with either Kalkwasser or a calcium reactor. However you do it, make sure you keep calcium levels high in invertebrate and reef aquaria.
