Clean your aquarium every one to two weeks, depending on tank size and how many fish you have

A full aquarium cleaning means removing about 25 percent of the water, scrubbing the glass and decorations, and rinsing the filter. You do not need to empty the tank or remove the fish. The bacteria that keep your tank healthy live in the filter and gravel, not in the water itself, so a partial water change actually preserves the balance while removing waste that builds up between cleanings.

Small tanks (under 20 gallons) need cleaning every seven to ten days because waste accumulates faster in less water. Larger tanks (40 gallons and up) can go two weeks between cleanings. If you have a heavily stocked tank or poor filtration, clean more often. If you notice algae growing thick on the glass or the water looks cloudy, clean sooner rather than waiting for your scheduled day.

Key Takeaways

  • Remove 25 percent of the water using a siphon or gravel vacuum, which also pulls debris from the bottom of the tank.
  • Scrub the glass walls and any decorations with an algae scraper or soft brush, using only water — never soap or chemicals.
  • Rinse the filter media under tap water to remove trapped waste, but do not replace it unless it is torn or falling apart.
  • Refill the tank with fresh water at the same temperature as the tank water, and add dechlorinator if your tap water is chlorinated.
  • Do the entire cleaning in 30 to 45 minutes so the tank does not sit with low water levels for too long.

What you need before you start

Gather a bucket (five-gallon size works well), a siphon or gravel vacuum, an algae scraper or soft-bristled brush, and a clean cloth or sponge. You will also need dechlorinator if your tap water contains chlorine — most municipal water does. Test your tap water temperature with a thermometer before you start so you can match it to your tank water when you refill.

Do not use soap, bleach, or any cleaning chemicals inside the tank. These kill the beneficial bacteria and can poison your fish. If you have stubborn algae or mineral buildup, plain white vinegar on a cloth works for glass, but rinse thoroughly with water afterward. For decorations, hot water and a brush are usually enough.

Step-by-step cleaning process

Step 1: Remove the water. Use a siphon or gravel vacuum to pull water out of the tank into your bucket. A gravel vacuum is better because it sucks up debris from the bottom while removing water. Push the vacuum head gently into the gravel in several spots around the tank. Remove about 25 percent of the total water — for a 40-gallon tank, that is 10 gallons.

Step 2: Scrub the glass. Use an algae scraper on the inside walls to remove green or brown film. Scrape gently so you do not scratch acrylic tanks (glass tanks are tougher). Wipe the scraped-off algae away with a clean cloth. Do the front, back, and sides. Skip the corners if algae is light there — some algae is normal and actually helps absorb nitrates.

Step 3: Clean decorations. Remove any rocks, plants, or ornaments that have visible algae or waste buildup. Scrub them under running tap water with a soft brush. For live plants, rinse gently without scrubbing the leaves. For plastic plants and ornaments, scrub more firmly. Put them back in the tank once they are clean.

Step 4: Rinse the filter. Turn off the filter and remove the filter media (cartridge, sponge, or floss). Rinse it under tap water, squeezing gently to release trapped waste. Do not use hot water or soap. If the media is torn, falling apart, or so clogged that water will not flow through it, replace it with a new one. Otherwise, put it back in the filter housing and turn the filter back on.

Step 5: Refill the tank. Fill your bucket with fresh tap water and add dechlorinator according to the bottle instructions. Let it sit for a minute, then slowly pour it into the tank. Pour slowly so you do not disturb the gravel or stress the fish. Fill until the water level is back where it started.

How often to replace the filter versus rinse it

Rinse the filter media every time you clean the tank. Replacement depends on the type. Sponge filters last three to six months before they break down. Cartridge filters (the pleated kind) last four to eight weeks. Floss or loose media lasts two to four weeks. These timelines assume you rinse the media every week — if you skip rinsing, they clog faster and need replacement sooner.

You will know it is time to replace when water flow slows noticeably even after rinsing, or when the media is visibly torn or disintegrating. Some filters have two cartridges so you can replace one while keeping the other running, which preserves more of the beneficial bacteria. If your filter has this option, replace one cartridge at a time rather than both at once.

Cleaning without removing your fish

You do not need to move your fish to a separate container during a routine cleaning. The fish can stay in the tank the whole time. They may hide when you are scrubbing, which is normal. Avoid sudden temperature changes — if your refill water is much warmer or colder than the tank, the fish can go into shock. Always match the temperature before pouring.

If you are doing a deep clean because the tank is very dirty or you are treating a disease, you may want to move the fish temporarily. Use a clean bucket or temporary container with some of the old tank water in it. Keep them there for no more than an hour. Do not use soap to clean the temporary container — rinse it with hot water only.

Signs your tank needs cleaning sooner than scheduled

Cloudy or milky water means bacteria or waste is building up faster than your filter can handle. Clean the tank and check that your filter is running and not clogged. A strong smell — not just a fishy smell, but something foul — means waste is decomposing. Clean when ready and check for dead fish or uneaten food hiding in the gravel.

Thick green algae on the glass or decorations is not an emergency, but it blocks light and uses up oxygen. Clean it off. Brown algae (diatoms) is harmless and usually means the tank is new or the lighting is low. If your fish are gasping at the surface or hiding constantly, the water quality has dropped — do a partial water change right away and check your filter.

Common mistakes that harm your tank

The biggest mistake is replacing the filter cartridge too often. Many people think they need a new one every week, but that kills the bacteria colony that keeps the tank stable. Rinse and reuse the same cartridge until it actually falls apart. Another mistake is using tap water without dechlorinator. Chlorine kills fish and bacteria. If you forget the dechlorinator, let the water sit in an open bucket for 24 hours — chlorine evaporates on its own.

Do not scrub the gravel too hard or vacuum it so aggressively that you suck up the beneficial bacteria. A gentle pass is enough to remove visible waste. Do not change more than 50 percent of the water at once, even if the tank is very dirty — large water changes shock the fish and destabilize the bacteria. If the tank is extremely dirty, do a 25 percent change, wait three days, then do another one.

Frequently Asked Questions

Can I use bottled water instead of tap water?

Yes, but it is expensive for regular cleanings. Bottled water is useful if your tap water is very hard or has high chlorine levels that bother your fish. For routine cleanings, tap water with dechlorinator works fine and costs almost nothing. If you use bottled water, you still need to match the temperature to avoid shocking the fish.

What if I do not have a gravel vacuum?

A regular siphon works, but you will miss the debris in the gravel. You can also use a turkey baster to suck up visible waste from the bottom, then use a cup to remove water. It takes longer, but it works. A gravel vacuum costs 15 to 30 dollars and saves time on every cleaning, so it is worth buying if you plan to keep the tank long-term.

How do I know if my filter is working properly?

Water should flow smoothly through the outlet. If the flow is weak or stopped, the filter is clogged — rinse the media. If the filter is running but the water is still cloudy after a week, the filter may be too small for your tank or you are overfeeding. Check the filter size matches your tank volume on the box, and reduce food to what the fish eat in two minutes.

Is it okay to clean the tank more than once a week?

Yes, if you want to. More frequent cleaning keeps the water clearer and removes waste faster. The downside is that you risk removing too much of the beneficial bacteria if you are too aggressive with the gravel vacuum. Stick to gentle cleaning if you clean more than once a week, and always rinse rather than replace the filter.