In aquarium hobbyist practice we usually have to use tap or well water, which may have very different characteristics. From the chemistry point of view, water is hydrogen dioxide. It consists of 2 parts of hydrogen and 1 part of oxygen - H2O. It contains many dissolved substances (free oxygen - 21 %, nitrogen - 76 % and carbon dioxide - 0.3 %). Bordering substrate, plants, fish, decaying substances and alkaline-earth metals water acquires new qualities.
Thus, first of all, the tank water should contain neither metals, nor a big amount of magnesium or calcium salts, nor any other components that can do harm to the aquarium inhabitants.
In the countryside you have to take a well, a river or lake water. Before filling the tank, heat water 152 �F high to get rid of dangerous bacteria.
The water good for drinking, is also good for the tank, except for mineral water. The tap water we use in our houses in most regions has an average hardness within the limits 8-12 degrees the year round. Overbalance of chlorine in the tap water must be removed in one of the following ways: 1) leaving water in some non-metallic dish for 1-2 days (until the bubbles stop to appear); 2) by an active aeration (for 10-12 hrs); 3) by a filtration of the water through activated carbon; 4) by adding 1 g of hyposulphite (thiosulphite) per each 10 l, or by boiling it for 10 minutes (remember: the water will lose oxygen, so, before being poured into the tank, it must be aerated).
It is not recommended to use the pond water. Rain water or water from melted snow is unsuitable too if gathered in the town or nearby, since in contains great amount of solid, liquid and gas substances that can be dangerous for living things. In the country you can take such water, though dust and other agents must be filtered away.
Before using water from the natural sources it is reasonable to settle some low cost fish in it and watch how they feel for several days.
As the water is poured into the tank some complex processes start inside. At first, plant particles, separated during planting, begin to decay and a plenty of bacteria appear. So the water may drop from pellucid to cloudy-white. After some time most of bacteria die due to lack of food and the water becomes transparent again. Adding some water and substrate from a long living and safe aquarium, which already obtains a ready complex of essential bacteria, you speed up the establishing of fair conditions for the fish and plants in the new tank.
The normal function of the aquarium can be tested by smelling the water. It should have the odor of green hay. Any other scent (smell of ammonia, hydrogen sulphide) indicates bad processes to take place there. This means you must again clean the substrate very well, change a part of water and once again check if you properly follow tank keeping rules.
* The tank needs clear water that contains all essential microelements for life of aquatic plants and (in most cases) has the following characteristics: DH - 5-20 degrees, �� - 2-15 degrees, �� - 6,5-7,5.
Translated by Tatiana Karpova (Moscow)
(MSU, Biology faculture, Dep. zoology and ecology).