Used fish tanks collect debris, soil and grime on the glass. Some tanks also have hard water stains that are difficult to remove. Cleaning an empty fish tank requires a few supplies and effort as you scrub away the stains. You must use natural cleaning methods without the use of hard chemicals. Chemical applications will create a toxic environment for your future fish.
Items you will need
Rinse the aquarium with warm water to remove the surface layer of dirt and grime. Continue rinsing until the all the loose dirt is removed. Use a moderate pressure hose for the rinsing. A kitchen sink sprayer or a shower nozzle is effective for removing grime. Drain the water after the initial rinsing and wipe the glass with paper towels to remove all loose dirt the water failed to capture. After the initial cleaning, you are left with the hard stains.
Run an algae scraper over the glass to remove difficult grime and algae. Follow the scraper with the coarse end of a kitchen sponge and scrub with firm pressure to remove hard stains. Dip the sponge in water as necessary and continue scrubbing until the stains are broken. Wipe away loose grime with paper towels during the scrubbing process.
Sanitizing the Tank
Pour a cap full of bleach on a paper towel and wipe it over the aquarium glass. This will kill any living organisms and sanitize the tank. Only bleach the interior of the tank. The exterior does not require sanitizing. Set the tank outside in the sun for four hours and the bleach will break down and lose potency. It will not have any effect on the water or fish after exposure to the sun.
Preparing for Fish
As a final measure, clean the glass with a nontoxic aquarium glass cleaner. Specialty cleaning products are available through pet stores that deal with fish. Spray the cleaner on the glass and wipe it clean with a paper towel. This will make the glass clear and ready for your fish. The tank is now ready for gravel, water and your fish habitat.