I hope this gives you all the information you need:- Sorry it is a bit long...
Cleaning Your Aquarium
Performing Your Weekly 10-15% Water Change
For all of you who have asked about cleaning tanks... Cleaning your aquarium is a simple and straight forward task, and should not take very long. The better care you provide for your tank, the healthier your fish will be, the nicer your tank will look and the easier your tank will be to care for in the future. You should not need to take all the stuff out of the tank when you clean it, in fact, I would not recommend it. Every surface in the tank will grow some beneficial bacteria that are part of the biological filter. By removing and cleaning the decorations you stress (and may even kill) some of this bacteria, reducing the quality of your filtration.
When cleaning your aquarium, you should just remove part (10-15%) of the water and replace it with fresh, dechlorinated tap water (bowls and vases require larger water changes more often). While you are doing this, you should use your siphon to suck up some of the gunk that collects in the gravel and decorations. If you have an under gravel filter, it is very important to clean the gravel when you do your weekly water changes, this will prevent detritus and other decaying organic matter from blocking the passages between the pebbles and restricting water flow. Generally, you can clean 25-33% (1/4-1/3) of the gravel while siphoning out 10-15% of the water.
If you have algae growing on the surface of the tank or ornaments, you should get an algae scraper of some sort and scrub the glass before removing water. Many varieties of algae scrapers or scrubbers are available at your local pet store. For additional cleanliness, you could get algae eating catfish and/or scavengers to pick up some of this work for you, however, having catfish in the tank does NOT mean that you don't need to clean. In fact, algae eaters and catfish, like any other fish, will add to the biological load of your tank and increase maintenance requirements.
Catfish or no catfish, I recommend doing 10-15% water changes once a week for the life of your aquarium. Once you get into this habit, it is not really that much work.
If you have to clean out the filter(s) do not change all the media (cartridges, sponges, carbon packets, etc.) at once, as this will remove the majority of your biological filter, causing the tank to have to go through a cycling period again to get bacteria reestablished. Rinse any new filter media in cool running water before introducing it to the system (unless the instructions for the filter media specifically state not to).
Once you have siphoned 10-15% of the water from your tank, you will need to fill it again. The easiest and neatest way to do this, is to use a siphon to siphon water from a bucket into the tank. This will tend to reduce spilling and messing up the gravel and decorations. Use a bucket that has never had detergents or household chemicals in it (we recommend getting a bucket specifically for use for aquarium chores) and fill it with water. The water should be close to the temperature of the tank water that you just took out (the average person can tell temperature differences within 1/2 degree Fahrenheit with their hand, so just feel the water to see if it is the same). Use a chlorine or chloramine remover to prepare the water for introduction into the tank. Place the bucket somewhere higher than the top of the fish tank, and get your siphon going again and in just a couple of minutes, you should have a full tank. Be sure to watch the siphon, in case the hose gets bumped out of the tank, or if there is enough water in your bucket to overfill the tank. Remember, there needs to be some space between the top of the water and the aquarium cover, because your fish rely on oxygen exchange at the surface of the water in order to be able to breathe.
Do not just "top off the tank" to replace water that "disappears." This water that is disappearing is evaporating, and it leaves behind all the impurities that were in it to begin with. This means that as you just top off the tank, you are making your water harder until it will eventually no longer be able to support fish. Additionally, if there are even trace amounts of heavy metals or other toxic substances in the water, you are giving your fish more and more of these every time you top off the tank. Most municipal water systems have at trace levels of at least one potentially hazardous substance, but in minuscule amounts these should never be trouble for you or your fish. Furthermore, by not removing water from the tank from time to time, you allow build up of waste products not removed by the filter (such as Nitrate), which are potentially hazardous to the fish and encourage algae growth.