Water Hardness in fresh water aquarium

Introduction

The fish we raise in our aquariums come from different parts of the world where they inhabit waters with specific chemical characteristics, in which the species evolved over time, and for which they are adapted. It is necessary to know a little about the needs of the species that we want to breed, in order to give the fish a habitat with conditions similar to their environment of origin

Hardness (general hardness - GH)

Hardness is a measure of calcium and magnesium ions in water. Hard water is often sourced fromlimestone aquifers, rich in CaCO3.

Most water test kits give the result in units of CaCO3, which means that the hardness is equivalent to that much CaCO3 in the water, but it does not mean that it must come from CaCO3. The most common way of expressing hardness is through "degrees of hardness" (dH - degrees hardness). Each degree of hardness is equivalent to 10 mg of calcium oxide (CaO) per liter of water.

The concept of hardness is important for the maintenance of species that are more sensitive and demanding in terms of water quality, such as discus, which should preferably be kept in soft water, and African cichlids, which originate from very hard water habitats. .

Generally, soft water is acidic, while hard water is alkaline, but this relationship is not mandatory.

Carbon Hardness - KH (buffering)

It is the measure of bicarbonate (HCO3-) and carbonate (CO3--) ions in water. As KH tests cannot be unique to carbonate and bicarbonate ions, they actually measure the alkalinity of the water, which is mainly due to the presence of these ions in the freshwater aquarium.

Alkalinity is a measure of the total buffering capacity of the acid, that is, of all the anions that can bind free H+ ions in the water, thus preventing the pH from dropping. In the freshwater aquarium, the terms "carbon hardness", "buffering capacity" and "alkalinity" are used interchangeably.

When the aquarium has some carbon buffering capacity, bicarbonate ions will combine with excesshydrogen ions to form carbonic acid (H2CO3) which will slowly dissociate into CO2 and H2O.

Over time, as carbon ions are used up, the buffering capacity will decrease, and steeper drops in pHwill be noticed.

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