If guppies are fed sparingly with a high quality food and regular water changes are performed, cleaning tanks and filters should be reduced to a minimum. I use two sponge filters in every tank and once a month put one of them through the washing machine (no soap!) with a little bleach added. I wipe down the sides of the tank when I transfer guppies in or out of the tank. The only time I bleach a tank is when the tank goes bad, usually the result of overfeeding my guppies.