Clean your aquarium every one to two weeks by removing debris, changing part of the water, and scrubbing the glass and decorations

A clean tank keeps your fish healthy and the water clear. The basic routine takes 20 to 30 minutes and involves three main tasks: removing waste from the bottom, replacing some of the old water with fresh water, and wiping down surfaces where algae builds up. You do not need to empty the tank completely or remove the fish—in fact, doing so stresses them and can harm the bacteria that keep the water safe.

How often you clean depends on tank size and how many fish you have. A small tank with many fish needs cleaning every week. A larger, lightly stocked tank can go two weeks between cleanings. If the water looks cloudy or smells bad, clean it sooner.

Key Takeaways

  • Do a partial water change of 20 to 30 percent every one to two weeks, removing old water and replacing it with fresh water treated with dechlorinator.
  • Use a gravel vacuum to suck debris from the bottom without removing the fish or draining the tank completely.
  • Scrub the glass walls and decorations with an algae scraper or soft brush to prevent buildup that blocks light and harms water quality.
  • Never use soap, bleach, or tap water alone—these kill the beneficial bacteria that keep ammonia and nitrite from poisoning your fish.
  • Clean the filter media in old tank water you removed, not under the tap, to preserve the bacteria living in the filter.

Gather your cleaning supplies before you start

You need a few inexpensive items, most of which you probably already have. A gravel vacuum (also called a siphon or aquarium vacuum) is the most important tool—it removes waste from the bottom while you refill. A basic model costs $15 to $30 and attaches to a bucket. You can also use a straightforward siphon hose if you already own one.

For scrubbing, use an algae scraper with a plastic or rubber blade—never metal, which scratches acrylic tanks and can rust. A soft-bristled aquarium brush works well for decorations and hard-to-reach corners. Keep a clean 5-gallon bucket just for the tank; never use one that held chemicals or soap. Fill it with tap water and treat it with dechlorinator before adding it to the tank—chlorine in tap water kills fish and beneficial bacteria. Most dechlorinator costs $5 to $15 and lasts months.

Have old towels or a wet-dry vacuum nearby to catch spills. If your tank has a filter, you may also need a small brush or old toothbrush to clean the filter media, though you will rinse it in old tank water, not tap water.

Remove debris from the bottom with a gravel vacuum

Start by placing your bucket on the floor next to the tank—it will catch the dirty water you remove. Submerge the gravel vacuum hose in the tank and position the intake tube (the narrow end) just above the gravel. Squeeze the bulb or use the priming method your vacuum came with to start the siphon. Water will flow out into the bucket.

Move the intake tube slowly across the bottom of the tank, hovering just above the gravel. The suction will pull up waste, uneaten food, and dead plant matter without removing the gravel itself. Spend extra time in corners and under decorations where debris collects. Avoid sucking up small fish or plants—if your intake is too strong, move it higher or cover the end with a fine mesh screen.

Continue until you have removed about 20 to 30 percent of the water. For a 20-gallon tank, that is roughly 4 to 6 gallons. For a 10-gallon tank, remove 2 to 3 gallons. The exact amount matters less than the routine—removing some water regularly is better than waiting and removing a lot at once.

Scrub the glass and decorations to remove algae

While the bucket sits, use your algae scraper on the inside glass walls. Hold it at a 45-degree angle and scrape from top to bottom in overlapping strokes. You will see green or brown algae come loose and float in the water—the gravel vacuum will remove it when you finish. Pay special attention to corners and the back wall, where algae grows thickest.

For decorations, rocks, and plants, use your soft-bristled brush to gently scrub away algae. If algae is thick and stubborn, soak the decoration in a separate bucket of old tank water for a few minutes, then scrub again. Do not use hot water or soap. If a decoration is heavily coated and brushing does not work, you can remove it, soak it in a bucket with a small amount of white vinegar (one part vinegar to three parts water) for 15 minutes, rinse it thoroughly under tap water, and return it to the tank. Vinegar kills algae without harming fish.

Do not scrape the filter intake or heater—these have delicate parts. If algae builds up on them, a soft brush is enough.

Refill the tank with treated water

Prepare your replacement water before you add it. Fill your clean bucket with tap water and add dechlorinator according to the bottle's instructions—usually a few drops per gallon. Let it sit for a minute so the dechlorinator can work. If your tap water is very cold, let it warm to room temperature, or mix in a small amount of hot water. Fish are stressed by sudden temperature changes.

Slowly pour the treated water back into the tank. Pour it onto a plate or into your hand to break the flow and avoid stirring up the gravel and clouding the water. Fill until the water level returns to where it was before you started. If you have a filter with an intake tube, make sure the water level is high enough that the intake stays submerged.

Turn the filter back on if you turned it off. Check that all equipment—heater, air pump, filter—is running normally. The water may look slightly cloudy for a few hours as particles settle; this is normal and will clear on its own.

Clean the filter media without killing beneficial bacteria

Your filter traps waste and houses bacteria that convert ammonia into less harmful compounds. Cleaning the filter media is important, but the method matters. Never rinse filter media under tap water—chlorine and the force of the water kill the bacteria you need.

Instead, rinse the filter media in the old tank water you just removed. Swish it gently in the bucket a few times until the water runs clearer. If the media is very clogged, you can rinse it in a second bucket of old tank water. This keeps the bacteria alive while removing trapped waste.

If your filter has a foam or sponge insert, squeeze it gently in the old water rather than wringing it out hard. If it has a cartridge, hold it under the old water and use a soft brush to loosen debris. Replace the media only when it falls apart or stops letting water through—usually after several months of regular rinsing.

Establish a cleaning schedule you can stick to

Mark your calendar or set a phone reminder for every seven to fourteen days, depending on your tank size. A small tank (10 gallons or less) with several fish needs weekly cleaning. A medium tank (20 to 40 gallons) with moderate stocking can go two weeks. A large, lightly stocked tank may stretch to three weeks, but weekly is safer if you are unsure.

Between full cleanings, do a quick check every few days: look for uneaten food, dead plants, or cloudy water. Remove visible debris with a net. If the water smells bad or looks murky, do a partial cleaning even if it is not your scheduled day.

Keep a log of when you cleaned and what you noticed—algae growth, fish behavior, water clarity. Over time, you will learn the rhythm your tank needs. A consistent routine prevents the buildup that leads to poor water quality and sick fish.

Frequently Asked Questions

Can I use tap water straight from the faucet without dechlorinator?

No. Chlorine in tap water kills fish and the beneficial bacteria in your filter and gravel. Even small amounts harm delicate fish. Always treat tap water with dechlorinator before adding it to the tank. It costs very little and takes seconds.

Do I have to remove the fish when I clean the tank?

No. Removing fish stresses them and can cause injury. Leave them in the tank while you clean. They may hide or dart around, but this is normal. The only exception is if you are treating the tank for disease or if a fish is injured and needs isolation.

What if the water is still cloudy after I refill?

Cloudiness usually clears within a few hours as particles settle and the filter catches them. If it lasts more than a day, the filter may be clogged or the tank may be overstocked. Check that the filter is running and consider doing another partial water change. If cloudiness returns quickly after every cleaning, you may be overfeeding—uneaten food decays and clouds the water.

How do I clean the glass without leaving streaks?

Use only an algae scraper and old tank water. Wipe the inside glass with the scraper, then use a clean, damp cloth to wipe the outside. Avoid glass cleaners and paper towels, which leave residue. If you want a streak-free shine, a microfiber cloth works better than paper towels.

Can I clean the filter and do a water change on the same day?

Yes, and it is fine to do both. Clean the filter media in old tank water, then do your regular partial water change. The only rule is never clean the filter in tap water, which kills the bacteria. Cleaning both on the same day does not harm the tank.