Increasing the carbonate hardness of the aquarium
The few lucky aquarists that have tap water free of harmful substances but rich in carbonates simply add those by replacing daily the water that evaporates. This operation, when possible, is only sufficient if there are only a few species that consume the calcium in the tank. In the case of an aquarium with a lot of corals, especially hard ones, the need for carbonates is so high that it cannot be replaced in this way. In recent years four systems have proved to introduce a sufficient amount of carbonates to the water.
The method of calcium hydroxide does not produce any practical carbonate to the aquarium. The hardness of the water is indirectly produced from the highest value of PH in the aquarium, where the carbon dioxide from the air above penetrates in the water (surface skimmer) forming the carbonate hardness. The high PH of hard water makes a very slow dosage recommendable. To measure the calcium and for the effect of the precipitation of phosphates this method is more than suitable.
Adding generators of carbonates
With this method you add carbonates to the aquarium using chemicals (powder or liquid). These are contained in the so called correcting salts. The aquarist should pay attention to which substances he chooses to use and keep in mind that for a marine aquarium; only those that have a pH 8 or higher are suitable (test the powder first by dissolving in water. Products with an acidity level under PH 8 should not be used. The advantage of this method is that its rapid and simple to use, the disadvantages are the costs and the continuous need to keep the doses under control, its ionic imbalance which is unavoidable even while continually changing the water and the values when reached are relatively modest.
Injection of carbon dioxide
This technique, which is very common in the American area, provides the aquarium with carbonates in the form of carbon dioxide, which in part transforms into carbonates. If hard water is used, and basic safety standards are applied (controlling the pH, which if too low blocks the entry of CO2 by closing the magnetic valve), this method can work and lead to the strengthening of the coral growth (BROCKMANN, 1999). This system should only be used, however, in aquariums with a very low concentration of nitrates and phosphates otherwise you can create problems with unwanted algae. Management costs are medium-high (refilling CO2 cylinder); purchasing costs are also similar (CO2 cylinder, pressure regulator, needle valve and pH regulator).
The Calcium Reactor
This newest accessory, very fashionable, expands the use of the technique of injecting carbon dioxide. The water is enriched and therefore with a much lower pH value, it reacts in a container of calcareous material. This melts slowly, adding calcium carbonates to the water in the aquarium. The advantage is its high efficiency, its disadvantages are the high purchasing costs (calcium reactor + earlier components) and the risk of algae problems. In aquariums with high values of nitrates and phosphates, there is often, after the installation of the calcium reactor, an exaggerated growth of annoying green algae. Recommendations, such as to insert the water outlet of the reactor directly into the skimmer (it is always of pH values from 6.0 to 6.05), don’t lead to much, since when using this system only a part of the excess carbon dioxide is removed. There have been nevertheless for sometime new types of calcium reactors whose output of water is characterized by pH values much higher, the risk of algae while using these new types of machines is much lower.
How do you measure the carbonate hardness
Titration tests, commercially available for carbonate hardness normally provide satisfactory measurements. In contrast to other tests (pH, nitrates etc.) they remain stable and their accuracy is more than sufficient for a normal aquarium. We need to however always consider their margin of error which is between 1 and 2° dKH. It is advisable to pay attention to certain factors:
Never perform an analysis of turbid water, this can significantly distort the results by raising the values. You must wait until all the sediments are deposited and focus the analysis only on the clear water drawn from the container.
Never perform the test if the water is at a high temperature or if it has a high pH value. The tests work better if there are normal conditions for an aquarium (25°C, pH 6-8). Keep the tests in a dark place. Close the tests immediately after use to avoid contamination. Always follow the instructions carefully.