Each environment is individualized by criteria such as size, filtration, species, bio load and the Aquarist. Unlimited variable can arise through a multitude of causes. Therefore we offer most commonly followed practice for maintaining a healthy aquatic environment.
Assuming the environment has all the types of filtration necessary ie. Biological, Chemical and Particulate, the rule of thumb is to change no more than 15% of the water, by means of a gravel vacuum or equivalent every month. At the same time period, replace your chemical and particulate media. Beyond this, your focus is purely aesthetic. Sloping of gravel, turning of decorative rock or structure. Trimming live plant growth or a simple algae wipe is a great way to wet your elbows and enjoy the hobby.
As a general rule - less is better. Small alterations to an environment is more easily adjusted than large dramatic change.
As always, you are welcome to step in to Aquatropics for a tank cleaning demo anytime.