Oliver Knott: hardening stones in the aquariumHow to test hardscape for lime
In this video, the well-known German aquascaper, Oliver Knott explains how to test the lime content of various types of stones. As a means of determination, oak extract is drizzled on various, assorted stones such as Ohko, Lava and Seiryu. Oak extract is available as an accessory in aquaristics and serves us as acid in our experiment. If you sprinkle some of the liquid on calcareous stones, it will cause a chemical reaction, perceptible as a visible blistering and bubbling on the stone. This reaction does not occur with non-calcareous stones.
Since the majority of aquatic plants, tropical, ornamental fish and also shrimp prefer soft, acidic water, an aquarist should prevent everything able to harden the water in his aquarium. Important, however, is the following point: calcareous stones will only then significantly harden the water when a CO2 system is used. If there is no carbon fertilization via CO2, the influence on the water parameters can be neglected. This is due to the fact, that with the introduction of carbon (CO2), small quantities of carbonic acid are formed. This reacts with the lime embedded in the stones and breaks down the solid limestone. This results in calcium carbonate (Ca2+), which increases the total hardness (GH) of the water, and carbonates (HCO3-), which increase the carbonate hardness (KH) in the aquarium.
Handling of calcareous stones in soft water
If you want to use hardening stones for aesthetic reasons in a plant aquarium or aquascape and still get as soft and acidic water parameters as possible, there are several ways to influence that. As explained by Oliver Knott, regular, big water changes with soft freshwater are a remedy. Also the use of active substrate - soil - can help depriving the water of minerals to get a lower ph-value as well as lower carbonate hardness and total hardness.
Another possibility is offered by the company ADA. softenizer can provide for soft and acidic water in continuous operation in the aquarium. This special glassware is filled with ion exchange resin, which continuously reacts with the water and reduces hardness.
By the way: in our guide "hardscape" we have listed all types of stone from our online shop, sorted from neutral to hardening.