Question

We do not clean ponds or lakes, but an aquarium needs to be cleaned. Why?

Answer 1

An aquarium is an artificial and incomplete ecosystem i.e., it is a man-made ecosystem and it does not contain all the components of a natural ecosystem. For example, it does not contain soil and decomposers that break down the organic matter into simpler inorganic substances and act as cleaner. So, due to lack of cleaners, aquarium needs to be cleaned. In contrast, ponds or lakes are complete and natural ecosystem with all the components that keep them clean. So, they are self-sustaining ecosystems.