Thank you for the info Waterdrop.Water changes are quite important. They remove hundreds of substances that we don't want to build up, substances that we also don't have the time or money to measure. Water changes also bring in various trace minerals that we do want to refresh, minerals that the fish depend on.
Any time we do a water change there is also an important opportunity to get rid of debris from the tank substrate (there will also be debris on plants and decorations but the substrate collects the most.) If we allow debris to build up for too long in the tank, the action of heterotrophic (not the same as the autotrophic bacteria in our filters) bacteria will break down so much of it that we will be in danger of small ammonia spikes that we might not see.
The most effective habit for reducing the problem of substrate debris is to use a gravel-cleaning siphon for your water changes. This is simply a device that has a cylinder (usually clear) attached to the end of the hose that goes in to the tank. As the siphon pulls water out of the tank you gently plunge the cylinder down in the gravel and the suction will pull the gravel part-way up the tube and then allow it to drop back down in the tank. The debris comes loose from the gravel and flows on out with the water. You move the cylinder about the tank trying to get most of the places that don't have plants or decorations. If you have a sand substrate there is a somewhat different skill to perform the same function.
The most common beginner misunderstanding about water changes is to think they are so stressful to fish that they should be minimized or avoided. This is not true. Water changes are your friend and it is much better for your tank water to be kept changed often enough that your tank chemistry stays very similar to your tap water chemistry. This way, many problems can be solved via larger tap water changes if necessary.
~~waterdrop~~