How to Clean a Fish Tank or Aquarium

A fish tank is not cleaned like anything else in the house. Scrubbing it spotless with hot water and soap would harm the fish and kill the helpful bacteria that keep the water safe. Cleaning an aquarium means regular partial water changes, siphoning waste out of the gravel, scraping algae off the glass and gently rinsing the filter, all without upsetting the balance in the tank. This guide covers each step and a simple routine.

It follows the RSPCA’s advice on setting up and looking after a fish tank, and the maintenance guidance of Tropical Fish Hobbyist (TFH) Magazine. Fish species differ, so ask your aquatics shop or an aquatic veterinarian about your own fish and tank.

Why you do not deep clean a fish tank

The RSPCA explains that fish release ammonia into the water, which is toxic. A working biological filter lets beneficial bacteria grow, which convert ammonia to nitrite (also toxic) and then to nitrate, which is safer but still causes problems in high levels. Those bacteria live in the filter, so the aim is to remove waste without wiping them out. That is why the RSPCA says water changes are needed to dilute the waste the filter cannot break down.

What you need

• A gravel cleaner (siphon) and a bucket kept only for the aquarium
• An algae scraper or magnetic glass cleaner suited to your tank
• A dechlorinating product (water conditioner) for the new water
• Water test kits
• Old towels for drips

Never use soap, detergent or household cleaners on anything that goes in the tank, including the bucket. Even small traces of residue can harm fish.

Step 1: scrape the algae

• Do the glass first. TFH Magazine says to scrape before changing the water, so you can siphon out the algae you remove.
• Use the right scraper. TFH says razor-blade scrapers suit glass tanks, but acrylic needs special plastic blades to prevent scratches. A magnetic cleaner lets you clean the inside of the glass from outside.
• Watch for grit. TFH warns that grains of sand or gravel caught between the blade or pad and the tank will severely scratch glass or acrylic.

Step 2: siphon the gravel and change the water

1. Leave the fish in the tank. The RSPCA’s method is a partial water change with the fish left in place.
2. Push the gravel cleaner into the substrate and move it around. TFH says that by moving the tube through the substrate while siphoning out water, you can remove most of the organic waste from the tank.
3. Take out only part of the water. The RSPCA advises weekly 30% water changes to dilute the waste products the filter cannot break down. Its step-by-step instructions start by removing ten percent with a siphon, so ask your aquatics shop how much suits your tank.
4. Keep the old water in the bucket for rinsing the filter (step 3).

Step 3: rinse the filter in tank water

The RSPCA says to swish the filter sponge or media in the aquarium water you have removed, which clears it of solids, but never to wash it under the tap, as that kills the beneficial bacteria. It also says to keep the filter parts clean so the filter runs smoothly, including removing and cleaning the impeller. Unplug the filter before you take it apart, and follow its manual.

Step 4: refill with treated water

• Remove the chlorine. The RSPCA says chlorine in tap water is dangerous to both fish and bacteria, so add a dechlorinating product to the new water, or leave it standing for 24 hours.
• Match the temperature. The RSPCA says new water at a different temperature from the tank will shock the fish.
• Pour gently onto a plate or decoration so you do not churn up the gravel.

Test the water

The RSPCA points out that clear water does not always mean healthy water. It advises testing water quality once a fortnight with test kits, and says kits for ammonia and nitrite are essential. If tests show a problem, it advises bigger water changes and asking your aquatics shop for help.

Keep a turtle? Turtle tanks get dirty much faster, so see how to clean a turtle tank.

Outside the tank

• Wipe the outside glass and lid with a cloth dampened with plain water, and keep household sprays well away from the tank. The RSPCA warns that aerosol sprays and cigarette smoke can be toxic to fish, and says a lid can help prevent some pollution.
• Dust the hood and light with a dry cloth, with the power off.
• Mop up drips on the stand and floor straight away, so water does not damage wood or flooring.

For fingerprints and smudges on other glass in the house, see how to clean pet nose prints and drool off glass, but use only plain water on and near the aquarium.

A simple routine

• Every week: scrape the algae, siphon the gravel, change part of the water, and swish the filter media in the old tank water as needed.
• Every two weeks: test the water, as the RSPCA advises.
• Now and then: clean the filter impeller and wipe the outside of the tank, lid and light.

For other pet homes, see how to clean a reptile tank and how to clean a hamster, guinea pig or rabbit cage.

Keep cleanup supplies ready

Our Pet Cleanup Kit is made for dog and cat accidents on carpets and fabrics. Keep it, and every other cleaning product, away from the aquarium.

Frequently asked questions

How often should I clean my fish tank?

Do a partial water change and gravel siphon every week, and test the water every two weeks, as the RSPCA advises. Ask your aquatics shop how much water to change for your tank.

Should I take the fish out to clean the tank?

No. The RSPCA’s method leaves the fish in the tank while you siphon out part of the water.

Can I clean the filter under the tap?

No. The RSPCA says to swish the filter sponge or media in the aquarium water you have removed, never under the tap, as tap water kills the beneficial bacteria.

How do I get algae off aquarium glass?

Use an algae scraper or magnetic cleaner before your water change, with a plastic blade on acrylic tanks, and keep sand and gravel away from the blade so it does not scratch, as TFH Magazine advises.

Sources

• RSPCA: Fish environment
• Tropical Fish Hobbyist Magazine: Aquarium maintenance

This guide is general cleaning information, not veterinary advice. If your fish seem unwell or your water tests are off, ask an aquatics specialist or an aquatic veterinarian.