You should clean your tank every two weeks, but don't worry, cleaning your tank takes just 3 steps, that take a total of about 5 minutes. Before you start, you'll need a few things:
When cleaning your tank, you need to remove and replace about 20% of the water. For example, you should replace 4 gallons of water in a 20-gallon tank. Start out by filling a bucket with the amount of water you intend to replace. Make sure that this water is the same temperature as the water already in the tank to prevent shock. You may need to add some hot water to do this. Ensure that you add some water conditioner to remove the chlorine, then set it aside for step 2.
Use your algae scrubber to remove algae from all four sides of your tank. If your live plants have algae on them, gently rub it off with your fingers. Remove all decorations and try to clean them with the algae scrubber. If this doesn't work, you can soak your non-porous (plastic) decorations in a weak bleach solution (about 1 part bleach to 20 parts water) for about 20 minutes, then soak them in clean water for another 20 minutes to remove the bleach. Generously add water conditioner to remove the bleach (it will remove hypochlorite, the active ion in bleach). Make sure that the decorations don't smell like bleach before you put them back in the tank. Be very careful with this method! It may remove the ink from your decorations. Never try to do this with plaster decorations. More Algae Fighting Tips
Next, remove 20% of your tank's water with a gravel siphon. It is much simpler to measure the height of the tank and divide it by 5 rather than trying to measure how many gallons of water you are removing. If your tank is 10" high, remove 10"/5 = 2" of water. Never remove more than 1/3 of the water or it will damage your biological filter.
To operate your siphon, completely submerge it in your aquarium, and work all the bubbles out of the pipe. Set the second bucket (the empty one) on the floor under the tank. Now put your finger over the small end of the gravel vacuum, take it out of the tank, and hold it over the bucket. Make sure that the large end is still in the tank, and the small end is below the water level, and then release the small end. The water will start to flow out of the tank and into the bucket. Work quickly, digging the large end through the gravel. The gravel is too heavy to be sucked out, but the lightweight fish waste and uneaten food are easily removed. If the vacuum is removing the water too fast, or if the gravel is being pulled out, you can put your finger over the small end to adjust to flow.
Once you have removed 20% of the water, slowly pour the water from the first bucket, which you have prepared earlier, into the tank. Make sure that you pour the water in slowly so it won't scatter the gravel or uproot the plants.
Now that you've cleaned the inside of your tank, the outside is probably covered in watermarks. These are easy to remove. Fill the spray bottle with 1 part vinegar and 10 parts water, and use this solution to clean the outside of the tank.