No one enjoys doing water changes, so a filter that claims to eliminate the need for water changes is sure to grab a hobbyist’s interest. The fact is, regardless of the size of your aquarium or how great a filtration system you purchased, the biological and chemical processes that alter the chemical balance of the water continue to occur. Certain elements and compounds are removed from the water, while others build up. In addition, water loss due to evaporation is a normal process in aquariums. As water evaporates, the chemicals increase in concentration as you add new water. The chemical composition of the aquarium water will change over time and not for the better.
The easiest way to counter these processes is to do regular partial water changes. Though you can change the water as infrequently as once a month (exchanging a third to half of the water), the ideal would be to change about 15% of the water weekly.
For more information on how to change aquarium water, watch the video below.