How often should you clean your aquarium tank?

Depending on fish population and tank size, a freshwater should be cleaned anywhere from every day to once a month. If you have a lightly stocked aquarium, monthly 25% waterchanges will be fine. If you are very overstocked, then you should do waterchanges weekly or more. If you have just the right stocking level for your tank, every 2-3 weeks will suffice. You may have to do it more often if your aquarium is overstocked or if you have very messy or larger fish. General stocking guide is 1 inch of TROPICAL fish for every gallon of water and 1 inch of COLDWATER fish for every 3 gallons. This is because coldwater fish get much larger than tropical fish so they need more room and they create more waste. The reason you should do a partial water changes even if you have a filter system is because your filter contains bacteria that change ammonia (fish waste by-products that are harmful for the fish) into nitrItes (ammonia by-products that are just as harmful to fish) and there is another bacteria that changes nitrItes into nitrAtes (nitrite by-product that is not as harmful to fish). These nitrAtes can be removed and diluted with a partial water change. Simply replacing water that has evaporated isn't enough as the water that evaporated is pure and these harmful chemicals cannot be dissolved into a gas form. When you do a water change, never replace the filter at the same time as this can remove some of the beneficial bacteria. Be sure to clean your gravel at least every 1-4 months so that your tank doesn't look like a mudslide hit it.