Depending on the size of the tank, it is advisable to vacuum the bottom (yes really) once a week. Then drain about 25% of the water and replace it with new water (treated with anti-chlorine and a pinch of aquarium salt). Remember the food and waste in the tank decompose to form harmfull nitrates and ammonia that causes disease or fish deaths.
The fish tank is a closed biological system, what goes in does not come out except on the filter, and the water you drain. Do not drain all the water as a new biological system will then have to form. Good bacteria forms on the filter cloth, so when you clean the filter, wash it in the water you have drained from the tank. This will ensure that chlorine in tap water does not kill the good bacteria. The good bacteria acts the same way as the human body, it attacks and kills harmfull bacteria. By doing this you can keep the tank clean.
PS! And you can always see the fish :-)
60 mths ago