General Hardness influences Calcium levels in the blood, and the osmotic regulatory systems of fishes are affected by concentrations of dissolved salts.

The fishes that we keep in our aquariums originate from all over the world. This is when the pH abruptly drops, and for the newcomer to the hobby, it would seem like there was no apparent reason.

The other path that rainwater will take is over the surface, which is termed as surface run off, and will run directly into streams, rivers, and landlocked bodies of water, such as lakes. Natural water will also contain suspended and dissolved impurities, which is why it must be treated before it is fit for us to drink. Most natural waters contain dissolved salts, which are consequently found in tap water. Any changes in water chemistry will have a greater impact in the aquarium than in nature, due to a much lower dilution effect.

If GH is too low add calciferous materials such as pieces of limestone into your aquarium; or a little coral gravel into your filter; don't add too much at one time, and monitor until desired value is reached.

Although we like to regard our aquariums as a small-scale reproduction of life in a lake or river, we must consider the much smaller volume of water our fishes have to live in. The test is similar to the GH test, but with a different reagent (the substance used to react with your water in the test tube to obtain a result).

Hardness of natural water is caused largely by calcium (Ca) and magnesium (Mg) salts and to a small extent computer monitor arm by iron, aluminium, and other metals. It is because of this capacity to dissolve numerous substances in large amounts that pure water rarely occurs in nature.

Carbonate Hardness (KH), or Temporary Hardness is principally composed of bicarbonate ions (HCO3) and carbonate ions (CO3), and has the capacity to neutralise an acid, this is known as the buffering capacity.

The immediate aspect of this is that aquariums with soft water are more likely to suffer from the phenomenon known as pH crash. You MUST regularly monitor your water to guard against any build up of harmful pollutants, as well as its general condition. It is therefore necessary for the aspiring fishkeeper to have an understanding of how the chemistry and quality of the water varies from region to region. This is referred to as General Hardness (GH), or Total Hardness, and is a measure of all the dissolved salts in the water.

Natural bodies of water, such as lakes and rivers, are by nature very stable environments, their large volumes of water counteract any changes in water quality, and it is this dilution effect that makes such changes hardly noticeable. Fortunately, water is highly adept at dissolving gases and solids, and it is this ability to readily dissolve other substances that makes it able to support life (water will also readily dissolve pollutants, which must be controlled).
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If General Hardness is too high make sure there are no calciferous materials in your water, such as coral, lime, or chalk. Some of the water will infiltrate the soil, a part of which becomes soil moisture, which will evaporate directly, or be used by the roots of vegetation. High levels could irritate gill membranes, they may look slightly swollen, and the fishes may be seen flicking or rubbing in the water.

The hardness and pH of your tap water supply is the first thing you should evaluate, knowing this will enable you to choose fishes that would be suited to your water conditions. Tropical freshwater fishes have evolved to live in these stable conditions, and are therefore very susceptible to any change they may encounter in water chemistry. Alternatively water-softening products are commercially available.

Carbonate Hardness (KH) is expressed in terms of the amount of calcium carbonate (CaCO3) present in solution. Hardness is usually expressed in terms of the amount of calcium carbonate (CaCO3) present in solution, and is normally measured as parts per million (ppm).

As you probably know water is a compound of hydrogen and oxygen, at the ratio of 2:1, hence H2O, and although life is dependant on water, pure water will not support life.

As water falls to earth as rain or snow it will absorb from the atmosphere varying amounts of carbon dioxide and other gases, as well as traces of organic and inorganic matter, upon reaching the earth's surface, the water will follow two paths. Fishes will detect even the smallest decline in water quality, and will often show signs of irritation and stress.

The amounts of salts dissolved in the water determine whether it is hard or soft.

It is necessary to test for General Hardness so that it matches the original habitat of the species being kept. Carbonate Hardness stabilises water pH. Alternatively you will have to adjust the chemistry of your tap water to suit the requirements of the fishes that you choose. Water that is in constant contact with substances such as limestone or chalk tends to be hard, whereas water running over sandstone or granite for instance, is likely to be soft. Water must contain certain salts if it is to support life at all. You will need to understand and be able to alter your own local water to suit the needs of your fishes.Water is an essential part of fishkeeping equipment, and it is probably the most misunderstood, many of the problems that occur in the freshwater aquarium are usually associated with water quality. Water that overcomes these forces in the soil profile will percolate deeper and become a part of the groundwater reservoir, the surface of which is known as the water table