How to Clean a Fish Tank: A Beginner’s Guide

Regular, partial cleaning removes waste and keeps the aquarium environment stable. It is not a full reset: beneficial bacteria on the filter and other surfaces help process fish waste, so replacing all the water or scrubbing everything can harm the tank’s biological balance. The right routine depends on the tank’s size, stocking, filtration, and water-test results.

Before you begin, check that the aquarium is running normally and that you have a safe place to put the removed water. If fish are gasping, injured, or showing other signs of illness, contact a veterinarian rather than treating cleaning as a diagnosis.

What You’ll Need

A clean aquarium bucket used only for fishkeeping—never one exposed to soap or household cleaners.
A siphon or gravel vacuum suited to your tank, plus a clean algae scraper or aquarium-safe sponge.
Water conditioner that treats chlorine and chloramine, used according to its label.
A thermometer, if available, to help match replacement water to the aquarium.
Optional: aquarium test kits for ammonia, nitrite, nitrate, and pH.
A towel to catch splashes.

Step-by-Step

Prepare the work area. Wash and dry your hands, then unplug equipment that could be exposed to water while you work, following its instructions. Keep electrical plugs and connections dry. Do not use soap, glass cleaner, or household cleaning products on anything that will go into the tank.
Check the tank before changing water. Look at the fish, water level, filter flow, heater, and decorations. If you have test kits, check water quality and record the results. A routine partial change is often around 10–25% of the tank’s volume; test results and tank conditions may call for a different schedule or amount.
Scrape the inside glass. Gently remove algae with an aquarium-safe scraper or sponge. Check that the tool has no grit trapped in it, which could scratch the glass. Avoid metal blades on acrylic tanks unless the tool is specifically approved for acrylic. Keep loose algae from drifting into the filter intake.
Siphon out water and debris. Start the siphon as directed by its maker, directing the outlet into the dedicated bucket. Move the gravel-vacuum end over sections of the substrate to lift out waste and uneaten food. Work gently, especially around plants and fish; do not churn the whole substrate deeply at every cleaning. Stop when you have removed the planned amount of water.
Clean decorations only as needed. If an ornament has visible debris or algae, swish it in the bucket of aquarium water you removed and wipe it with a clean, aquarium-only tool. Avoid scrubbing every decoration at once or removing all surfaces where beneficial bacteria live. Never use soap or disinfectant.
Prepare replacement water. Use water appropriate for your aquarium and treat it with conditioner according to the product label to neutralize chlorine or chloramine. Aim for a temperature close to the tank’s; a thermometer helps. Large differences in temperature or water chemistry can stress fish.
Refill slowly. Pour conditioned water gently onto a clean dish or other aquarium-safe surface to avoid digging up substrate or startling fish. Do not overfill; leave the tank at its normal operating level.
Restart and check equipment. Plug in and confirm the filter, heater, and other equipment are working as intended. Make sure the filter is moving water and the heater is submerged to the level specified by its manufacturer. Check for leaks, then observe the fish for a few minutes.
Clean the filter cautiously. Do this only when flow is reduced or maintenance is due, not automatically at every water change. Follow the filter maker’s directions. If reusable media needs rinsing, gently swish it in removed aquarium water—not tap water—and never replace all biological media at once. Do not run the filter without water if its instructions prohibit it.

Common Mistakes

Changing all the water: A complete water replacement can create abrupt changes and remove much of the established biological balance. Routine maintenance is usually a partial change, with the amount guided by testing and the aquarium’s needs.

Taking fish out for routine cleaning: Catching and moving fish adds stress and is generally unnecessary. Leave them in the aquarium unless a specific emergency or veterinary instruction requires otherwise.

Washing filter media under the faucet: Untreated tap water may contain chlorine or chloramine that harms beneficial bacteria. Use removed aquarium water when rinsing reusable media, and keep biological media wet.

Cleaning everything at once: Deep-cleaning the substrate, replacing media, and scrubbing every surface in one session can disrupt the aquarium’s bacterial community. Do only the maintenance needed and avoid sterilizing tank items.

Adding untreated or mismatched water: Conditioner does not make a large temperature difference safe. Treat new water as directed and add it at a similar temperature to the tank.

Tips

Keep a simple log of water changes, test results, and unusual observations. It can help reveal gradual changes that are easy to miss.
Use a dedicated bucket and tools; label them clearly and store them away from cleaners and chemicals.
Remove uneaten food and dead plant material when noticed, rather than waiting for the next full maintenance session.
Clean only part of the substrate at a time if the aquarium is heavily planted or has a deep substrate.
Do not rely on water clarity alone. Water can look clear while ammonia or nitrite is present, so testing is useful when fish seem stressed or the tank is newly established.

Troubleshooting

The water turns cloudy after cleaning: A brief disturbance may stir up fine debris. Check that the filter is running and avoid another deep clean. Test water if cloudiness persists, worsens, or fish appear distressed.

Fish gasp, act unusually, or struggle after a water change: Check that the filter is working and verify the replacement water was conditioned and close in temperature. Test ammonia and nitrite if you can. If distress continues or you suspect illness, injury, or poisoning, contact a veterinarian promptly; do not add medication or chemicals without appropriate guidance.

The filter flow is weak: Check for a blocked intake, kinked tubing, or clogged mechanical media, and consult the filter instructions. Rinse reusable media gently in removed aquarium water when needed. Do not discard all media or let biological media dry out.

You added untreated water by mistake: Use an aquarium water conditioner according to its label as soon as possible, and monitor the fish and water quality. If fish show distress, contact a veterinarian.

The siphon will not start: Follow the siphon’s instructions; many models have a hand pump or need a particular tilt or priming method. Keep the bucket below the tank’s water level and stop if the hose slips or water approaches an electrical connection.

Frequently Asked Questions

How often should I clean a fish tank?

There is no single schedule for every aquarium. Test water and watch the tank; many setups need a partial water change about weekly or every other week, but stocking, tank size, plants, and filtration affect the routine.

How much water should I change?

A common routine range is about 10–25% at a time. Use test results and the aquarium’s condition to guide the amount, and avoid sudden, unnecessary full water changes.

Should I take the fish out while cleaning?

No, not for ordinary maintenance. Leaving fish in the tank avoids the added stress of catching and moving them.

Can I use tap water in my fish tank?

Often, but it must be treated for chlorine or chloramine, and its temperature should be close to the aquarium’s. Follow the conditioner label and consider testing source water if you have persistent water-quality problems.

Do I need to clean the gravel every time?

You can siphon visible waste from sections of gravel during water changes, but do not deeply churn the entire substrate at every cleaning. In planted tanks, avoid disturbing roots and beneficial surfaces unnecessarily.

When should I clean or replace filter media?

Maintain it when flow drops or the manufacturer recommends it. Rinse reusable media gently in removed aquarium water; replace media only as directed and avoid changing all biological media at once.

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