How to Clean a Dirty Fish Tank

Healthy and happy community aquariums require clean, safe environments

Illustration on how to clean an aquarium.

The Spruce/Melissa Ling

If you tear down a dirty fish tank, you'll lose all the beneficial bacterial colonies that eliminate the animals' waste. Don't start over unless your tank is in extremely bad condition. However, you can clean your existing aquarium without completely breaking it down. With a little elbow grease and a few simple cleaning supplies, your aquarium can be shipshape again in no time.

What You'll Need

  • Algae scraper/pad
  • Razor blade (plastic blade for acrylic tanks)
  • Bleach
  • Water siphon (gravel vacuum)
  • Bucket (use a new bucket that is for aquarium use only)
  • Lime remover/glass cleaner (made for aquariums)
  • Filter media
  • Filter brush
  • Old bath towels
  • Paper towels
  • Chlorine remover (aquarium water conditioner)

Clean your aquarium in the following order:

  1. Inside glass
  2. Decorations (rocks, plants, etc.)
  3. Gravel
  4. Outside glass and fixtures
  5. Filter

Cleaning the Inside Glass

Start by giving the glass a good cleaning on the inside with an algae pad. There are a wide variety of algae scrapers on the market, from long-handled scrubbers to magnetic scrubbers.

Buy algae pads at a pet shop instead of the housewares department of a regular store. Although they may look the same, the housewares pads can have soap or chemical residue. That residue doesn't matter if you are cleaning your kitchen sink, but it can be lethal to your fish.

For stubborn residue on the glass, use a razor blade to scrape it off. Take care not to cut yourself. If your aquarium is acrylic, use a plastic razor blade, as standard razors will scratch the acrylic.

Cleaning Decorations and Rocks

Once the inside glass is clean, remove rocks, artificial plants, and decorations that have significant algae growth or are noticeably dirty. Do not clean them with soap or detergents. It's very difficult to completely remove soap, and even a trace can be harmful to fish. Usually, a good scrub with an algae scraper in warm water will remove the algae and dirt from rocks and plants.

For particularly stubborn cleaning problems, prepare a 10 percent bleach solution and soak the items for 15 minutes. Scrub any remaining residue off, rinse well in running water, and let air-dry to eliminate residual bleach. Don't put them back in the aquarium until there is no more chlorine smell present. You can calso rinse them in water that has dechlorinator (sodium thiosulfate) added to it to remove the chlorine.

Live plants can be bleached to remove algae from them. However, stem plants are not tolerant of bleaching. To bleach live plants prepare a 5 percent bleach solution, soak the plants for two to three minutes, then rinse well.

Leave the rocks, decorations, and plants out of the tank while you vacuum the gravel. That way none of the debris stirred up from the gravel will settle on them.

Be sure to get a new bucket and designate it for aquarium use only. If you use a bucket that has had soap or detergent in it, you could introduce unwanted chemicals into your aquarium.

Siphon to Clean Aquarium Gravel

Clean the gravel next, by using a water siphon to vacuum away the debris. There are several types of siphons available, all of which work essentially the same. The gravel vacuum should stir up the gravel and remove debris without sucking up the gravel. Be sure to vacuum the entire surface of the gravel thoroughly so that all debris is removed.

The water that is removed with the debris using the gravel vacuum is replaced with dechlorinated water, which performs a water change in your aquarium. Be sure the replacement water is the same temperature as your aquarium water. You should unplug your aquarium heater during water changes to prevent it from being exposed to air as the water level drops. A 25% water change is good amount for a monthly water change during cleaning.

Outside Glass and Fixtures

Once the inside of the aquarium is cleaned, clean the hood, light, tank top, and outside glass. Regular glass cleaners contain ammonia, which is toxic to fish. Standard lime cleaners are even more toxic. It is strongly recommended that you use vinegar or a cleaner designated as aquarium safe, and make sure you rinse the surfaces with a clean damp cloth.

Clean the Filter Two Weeks Later

Once the outside is clean, the rocks, plants, and other decorations may be returned to the tank. Now, wait a couple of weeks before cleaning the filter. Why wait? The major cleaning you just performed disturbed the beneficial bacterial colonies on the plants, rocks, and gravel.

Fortunately, many beneficial bacteria reside within the filter media, so you haven't completely upset the ecosystem. However if you changed the filter at the same time, you might trigger a dangerous ammonia spike because there aren't enough beneficial bacteria left to eliminate the toxins.

If you have filter media containing carbon, ammonia absorbers, or ion-exchange resins, it should be replaced if it's more than three weeks old. After a couple of weeks, the absorbing qualities of the media have been exhausted, and it no longer serves its purpose.

A medium that acts as a mechanical filter instead of absorbing toxins (i.e. ceramic rings, filter fiber, or sponges) should be gently rinsed to remove debris and returned to the filter instead of replaced. If care is taken to use water that is the same temperature as the aquarium water and the media is quickly returned to the filter, the bacterial colonies growing on them will not be lost entirely.

Don't forget to clean the filter tubing and other parts of the filter assembly. A filter brush will help clear out the sludge that builds up in all the small crevices.

Ongoing Maintenance

Once you've gotten your tank in shape, make sure you clean it on a regular basis so it never needs a major spring cleaning again. Scrape the glass weekly, vacuum the gravel every time you perform a water change, and clean any rocks or plants as soon as you see debris or algae on them.

Clean the filter monthly, either by replacing the media or rinsing it. While you are at it, soak your fishnets in a disinfectant solution to keep them clean and soft. With regular care, your aquarium will look beautiful all the time.