Join Date: Oct 2013
Location: Houston, Texas.
Essentially what a water change does is mimic the constant supply of freshwater that you would encounter in a lake, river, or stream. Because aquariums are a closed environment without this constant supply of fresh water, WE being the aquarists assume the role of mother nature. As stated above, plants complete a huge part of the nitrogen cycle. Even though your parameters are still reading good, there are several unmeasurable parameters in the tank that are either being depleted or building up, much in the same way that when water evaporates in a saltwater tank, the salt concentration rises. I am a firm believer that water changes are the single most important thing one can do for a tank. In 15 years, I have found that a weekly 30% water change is a good balance between practicality and functionality.