How to Clean a Fish Tank Properly

Regular maintenance removes waste, controls algae and helps keep water conditions stable. For most established freshwater aquariums, a partial water change and light cleaning every week or two is a useful starting point; the right interval depends on tank size, stocking, feeding and test results. Gather supplies first, and never use household cleaners in or around aquarium water.

What You’ll Need

A clean aquarium siphon or gravel vacuum and a bucket reserved for aquarium use
Water conditioner that treats chlorine and chloramine, used according to its label
A clean algae scraper or aquarium-safe sponge; use a plastic blade for acrylic tanks
A thermometer, if available, to compare replacement water temperature with the tank
Water test kit or test strips for checking parameters when needed
Clean hands or aquarium-safe gloves, with no soap, lotion or chemical residue

Do not use a bucket, sponge or scraper that has touched soap, detergent or other cleaning products. Unplug equipment before lowering the water below it or handling it, and follow its instructions.

Step-by-Step

Check the tank first. Observe the fish, water level, filter flow and heater. If a fish looks ill, injured or in pain, contact a veterinarian rather than trying to solve the problem with a deep clean. Test the water if fish are behaving unusually or maintenance is overdue; cleaning does not replace finding the cause of a water-quality problem.
Prepare replacement water. Fill the aquarium-only bucket with tap water and add conditioner for the amount of water being treated, following the product label. Adjust the new water to be close to the aquarium’s temperature. A sudden temperature change can stress fish, so do not add very cold or hot water.
Turn off equipment as needed. Unplug heaters and any equipment that could run dry or be exposed as the water level falls. Keep the filter running if it can operate safely at the current level; otherwise, switch it off briefly. Never handle electrical equipment with wet hands, and do not let a heater operate out of water.
Scrape the glass. Use an aquarium-safe scraper or sponge to loosen algae from the inside walls. Work gently, keeping sand or gravel away from the tool so grit does not scratch the glass. For acrylic, use only a tool labeled safe for acrylic. Avoid scraping silicone seams or forcing a blade into them.
Siphon out water and debris. Put the siphon outlet into the aquarium-only bucket and start the siphon according to its directions. Vacuum the surface of gravel in small sections, lifting food scraps and fish waste while avoiding deep disturbance of the whole substrate. For sand, hover just above the surface or use a gentle flow so the sand stays in the tank. Remove about 10 to 25 percent of the water for routine maintenance; a heavily stocked or messy tank may need a different schedule based on testing.
Clean decorations only if needed. Brush algae from removable decorations using aquarium-only tools and water taken from the tank. Do not scrub everything spotless or remove all surfaces at once: beneficial bacteria live on decorations, substrate and filter media. Never use soap, bleach or household disinfectant on items that will return to the aquarium.
Service the filter gently. Check the filter manufacturer’s instructions. If the media is clogged, swish or squeeze it gently in the bucket of removed aquarium water. Do not rinse it under untreated tap water, replace all media at once, or discard biological media simply because it looks dirty. Mechanical parts may need cleaning, but preserve the established biological media wherever possible.
Refill slowly. Pour the prepared, conditioned water into the tank gently, onto a plate or other clean surface if needed to prevent stirring the substrate. Keep the temperature close to the tank’s and do not fill beyond the aquarium’s marked or safe operating level.
Restart and check equipment. Plug equipment back in with dry hands. Confirm the filter is flowing, the heater is submerged as required by its instructions, and the thermometer reading is appropriate. Check for leaks, unusual noise or a filter that has not restarted. Observe the fish after the water change.

Common Mistakes

Replacing all the water: A full drain can cause abrupt changes and disrupt the aquarium’s stable conditions. Routine cleaning should usually be a partial change, with larger changes guided by test results or a specific problem.
Using untreated tap water: Chlorine and chloramine can harm fish and beneficial microbes. Condition new water before it enters the aquarium, following the conditioner directions.
Over-cleaning the filter: Sterilizing or replacing all filter media can remove beneficial bacteria that help process fish waste. Clean only what is necessary and preserve biological media.
Scrubbing the tank with household products: Soap and cleaning chemicals can leave residues that are unsafe for aquatic life. Use dedicated aquarium tools and water only.
Deep-cleaning the substrate every time: Aggressively stirring all gravel or sand can cloud the water and disturb useful bacteria. Vacuum gradually and focus on debris-prone areas.
Moving fish to a bowl for routine cleaning: Netting and transferring fish adds stress and is usually unnecessary. Leave them in the aquarium while siphoning carefully.

Tips

Keep a simple log of water changes, test results and equipment maintenance. It can help reveal a recurring issue such as excess feeding or a clogged filter.
Feed only what the fish consume promptly, and remove uneaten food when practical. Excess food breaks down into waste and can increase algae and water-quality problems.
Clean the aquarium in manageable sections rather than trying to make every surface look new at once.
Use test results to adjust the cleaning schedule. Tank size, fish load, plants and filtration all affect how quickly waste builds up.
Wash your hands before aquarium work and rinse them thoroughly with plain water. Keep lotions, sprays and cleaners away from the tank.

Troubleshooting

The water turns cloudy after cleaning: A little temporary cloudiness can follow substrate disturbance. Avoid another deep clean; check that the filter is running and test the water if cloudiness persists or fish seem distressed. Do not add clarifying chemicals without checking that they are suitable for the aquarium.

Fish gasp at the surface or act unusually: Check filter flow and water temperature, and test water parameters promptly. If there may be untreated tap water in the tank, use an appropriate conditioner according to its label. For signs of illness, injury, poisoning or pain, contact a veterinarian.

The filter will not restart: Check the outlet, intake and assembly against the manufacturer’s instructions. Do not let a heater run exposed while troubleshooting. If the filter stops for an extended period, keep its media wet in aquarium water and restore filtration as soon as possible.

Algae returns quickly: Review lighting duration, feeding and nutrient buildup, and test the water. Scraping algae removes what is visible but does not address its cause. Avoid drastic changes to lighting, fish load or water chemistry.

Replacement water differs in temperature: Add it slowly only when it is close to the tank’s temperature. If the difference is noticeable, adjust the prepared water before refilling rather than pouring it in all at once.

Frequently Asked Questions

How often should I clean a fish tank?

Many aquariums do well with a partial water change and light cleaning weekly or every two weeks. Use water tests, fish load and visible waste to set a suitable routine for your tank.

Should I take the fish out while cleaning?

No, not for routine maintenance. Cleaning around the fish avoids the stress and risks of netting and transferring them.

Can I use tap water in a fish tank?

Tap water can be used after treatment with a conditioner that handles chlorine and chloramine. Match its temperature reasonably closely to the aquarium before adding it.

Can I wash filter media in tap water?

Avoid untreated tap water, which may damage beneficial bacteria. Gently rinse or swish clogged media in water removed from the aquarium, and follow the filter’s instructions.

How much water should I change?

About 10 to 25 percent is a common range for routine changes, but the appropriate amount depends on test results and tank conditions. Avoid changing all the water as a standard cleaning method.

Do I need to clean a new aquarium the same way?

A new aquarium needs to be set up and cycled before it is stocked; routine cleaning alone does not establish a functioning biological filter. Follow reliable aquarium setup guidance and monitor water parameters as the tank matures.

Further reading: The Humane Society of the United States. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.