Feeding leads to a regular input of nutrients into every aquarium. As a result of excretion by the creatures living in the aquarium, 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, fish and plants enjoy a continual supply of fresh water, and waste products and inhibitors are washed away. To achieve a similar effect, part of the water in an aquarium requires to be replaced on a regular basis. This regular replacement of old, contaminated water with fresh water is crucial to the effective functioning of any aquarium - and of mini aquaria in particular.Unfortunately, fresh tap water is not directly suitable for aquaria, however, as it may contain substances which pose a threat to fish, shrimps, crabs and plants. Invertebrates are particularly sensitive to contaminants such as chlorin