A clean aquarium does not mean a healthy aquarium - there is a big difference

A healthy filtered aquarium is a largely self regulating environment for your fish, relying on healthy mechanical and biological filtration and suitable water chemistry parameters for the inhabitants.

Mechanical filtration

In essence this is simply the straining of suspended particles and debris to give the water a clean appearance.

Bilological Filtration

This is carried out  by populations of bacteria in your filter and substrate.  It it imperative these bacteria are kept alive for your fish to thrive.

Water Chemistry

There are many parameters that can be measured to ensure the water in your tank is suitable for your fish including pH, GH and KH