Water treatment & care

Changing part of the water on a regulat basis is crucial to maintaining the biological balance

An aquarium is a self-contained system. Feeding entails a continual input of nutrients into the water. As a result of excretion by the fish, over the course of time numerous waste substances and algae nutrients accumulate which even the best filter is unable to break down. Plant growth may start to flag, despite adequate fertilization. This is just to the liking of troublesome algae.
In nature, waste substances and inhibitors are transported away by the flowing water. In aquaria, they are removed by replacing part of the water on a regular basis.  This regular input of fresh water is crucial to the correct functioning of an aquarium.
Fresh tap water is not directly suitable for aquaria, however, as it may contain substances which pose a threat to fish and plants. Equally, important constituents of natural waters, such as humic substances, trace elements and organic colloids, are lacking in tap water.