A Step by Step Guide on How to Clean a Dirty Fish Tank

You peer into the murky water. Algae coats every surface, making each rock and plant slimy. Suddenly, a blurry shape takes form, and it’s swimming straight for you!

Don’t panic, it’s just one of your fish, begging you to clean its tank. Once a dirty fish tank gets out of hand, cleaning it can seem daunting.

Luckily it doesn’t have to be a chore. This step-by-step guide will show you how to clean a dirty fish tank, the easy way.

Step1: Clean the Inside of the Tank

To start your fish tank cleaning, use an algae pad to scrub the glass inside your tank. Avoid using regular household kitchen sponges or abrasive pads. These contain soap or chemicals that are harmful to fish.

For stubborn residue, you may need a razor blade. A metal blade is fine for glass tanks, but if your tank is acrylic be sure to use a plastic blade.

Step 2: Scrub Your Tank Decorations

Remove any rocks, plants, and decorations from your tank and give them a good scrub. Remember, don’t use soap or cleaning agents as these are harmful to fish.

For particularly stubborn patches, prepare a 10% bleach solution. Soak the items for 15 minutes, then scrub the loosened dirt off. Rinse thoroughly, then leave them out to dry so that residual bleach can evaporate.

Live plants can be removed and gently cleaned too. If they are very dirty, soak them in a 5% bleach solution for 2-3 minutes. Note that stem plants do not react well to bleach.

Step 3: Siphon the Substrate

Next, using a gravel vacuum, clean the gravel at the bottom of your tank.

Siphon the substrate until the water coming out of your gravel vacuum runs clean.

Unplug your aquarium heater to prevent it from being exposed to the air and overheating.

Pay careful attention to your water level. Don’t let it drop below 50%, even if your substrate is still dirty. Rather stop, and resume cleaning in a week or two.

Once your substrate is clean, replace your decorations.

Refill the tank with dechlorinated water.

Be sure the water is the same temperature as the water in the tank as sudden changes in temperature can shock your fish.

Step 4: Clean the Outside of the Tank

Wipe down the outside of your tank to remove dust and water spots.

Most glass cleaners contain ammonia and other nasty chemicals. To be safe, use a mixture of water and vinegar. Rinse the surface when done.

Step 5: Wait Two Weeks, Then Clean the Filter

Once you have a nice, clean fish tank, wait 2 weeks before changing the filter. This allows beneficial bacteria to recover. Learn more about how bacteria live in a mechanical filter.

Carbon, ammonia absorber, and ion exchange resin filters should be changed every 3 weeks.

If you have a mechanical filter, gently rinse it with water that is the same temperature as your tank water. This cleans excess dirt from the filter without killing off too much good bacteria.