Clean your aquarium on a weekly schedule for partial water changes and a monthly schedule for a full tank cleaning

Most aquariums need a 25 percent water change once a week and a thorough cleaning of the tank, filter, and decorations once a month. The exact timing depends on tank size, how many fish you have, and what kind of filter you run. A 10-gallon tank with five fish needs more frequent attention than a 55-gallon tank with the same number of fish, because waste builds up faster in smaller volumes of water. Overstocked tanks—those with too many fish for their size—may need water changes twice a week.

The weekly partial water change is the most important part of maintenance. Fish produce ammonia through their gills and waste, and even a good filter cannot remove it fast enough. Changing 25 percent of the water dilutes the ammonia and nitrite that accumulate between cleanings. Skipping weekly changes causes these toxins to spike, which stresses fish and can kill them within days.

Key Takeaways

  • Change 25 percent of your tank water every seven days to remove ammonia and nitrite that build up from fish waste.
  • Clean the filter media, decorations, and tank glass once a month, but do not replace the filter media with new media—rinse it in old tank water to preserve beneficial bacteria.
  • Smaller tanks (under 20 gallons) need cleaning more often than larger ones because waste concentrates faster in less water.
  • Tanks with more fish than the tank can comfortably hold may need water changes twice a week instead of once.
  • Test water parameters (ammonia, nitrite, nitrate) if fish show stress or if you are unsure whether your cleaning schedule is working.

Weekly Water Changes: The Core of Tank Maintenance

A weekly 25 percent water change is the single most effective way to keep your tank stable. Use a siphon or aquarium vacuum to remove water from the bottom of the tank, where waste and uneaten food settle. This removes not just the water but also the debris that would otherwise break down into ammonia.

Replace the removed water with fresh water that has been treated with a dechlorinator if your tap water is chlorinated. Let the new water reach room temperature before adding it, or add it slowly so the temperature change does not shock the fish. If you have a heater, the new water will warm up within an hour.

Some aquarists with heavily planted tanks or very light bioloads (few fish, lots of plants) can stretch to 10-day intervals, but weekly is the standard that works for most setups. If you notice algae blooming rapidly or fish gasping at the surface, move to twice-weekly changes until the tank stabilizes.

Monthly Deep Cleaning: Filter, Glass, and Decorations

Once a month, do a more thorough cleaning alongside your regular water change. Remove decorations, plants, and the filter media and rinse them in a bucket of old tank water that you siphoned out. Do not use tap water or soap—tap water kills the beneficial bacteria that live on these surfaces, and soap is toxic to fish. The old tank water is safe and contains the bacteria you want to keep.

Scrape algae off the glass with an algae scraper or a plastic card. Wipe the inside surfaces of the tank if algae has built up. Clean the filter intake tube and any visible debris from the substrate, though you do not need to remove all the substrate—just the top layer where waste collects.

If your filter has a mechanical stage (foam or floss that catches particles), rinse that in old tank water. If it has a biological stage (sponge or media where bacteria live), rinse it gently and do not replace it unless it is falling apart. The bacteria on that media are what keep ammonia from poisoning your fish, so preserving them is critical.

Tank Size and Bioload: Why Schedules Vary

Bioload is the amount of waste your fish produce. A 10-gallon tank with five goldfish has a much higher bioload than a 10-gallon tank with five tetras, because goldfish are larger and messier eaters. The smaller the tank relative to the bioload, the faster ammonia and nitrite accumulate.

A general rule: tanks under 20 gallons need weekly water changes without exception. Tanks 20 to 55 gallons can often hold to weekly changes if they are not overstocked. Tanks over 55 gallons with moderate stocking may stretch to 10 days between changes, though weekly is still safer. Heavily planted tanks with few fish can sometimes go longer because plants consume some of the nitrogen waste, but this is not a substitute for water changes—it is a bonus.

If you are unsure whether your schedule is working, buy a basic aquarium test kit that measures ammonia, nitrite, and nitrate. Ammonia and nitrite should always be zero. Nitrate should stay below 40 parts per million. If either ammonia or nitrite is above zero, increase the frequency of water changes.

Filter Type and Cleaning Frequency

The type of filter you use affects how often you need to clean it. A hang-on-back filter with a cartridge needs rinsing every two to three weeks. A canister filter can go three to four weeks between cleanings because it holds more media. An undergravel filter or sponge filter should be rinsed weekly or every other week.

When you clean the filter, do it during your regular water change so you can use the old tank water. Turn off the filter before you remove it, and work quickly so the beneficial bacteria do not dry out. If the filter media is clogged with brown sludge, it is restricting water flow and needs cleaning more often.

Signs Your Tank Needs Cleaning More Often

If you notice algae blooming rapidly, a cloudy film on the water surface, or a foul smell coming from the tank, the bioload is outpacing your cleaning schedule. Fish gasping at the surface or hiding constantly are also signs that ammonia or nitrite has spiked. Move to twice-weekly water changes when ready and do not skip them until the tank clears.

Uneaten food rotting on the bottom is another sign. If your fish do not finish their food in five minutes, you are overfeeding. Remove uneaten food with a net or siphon, and feed less. Overfeeding is one of the most common reasons tanks become toxic.

Seasonal Changes and Vacation Planning

In warmer months, fish metabolism speeds up and they produce more waste, so you may need to increase water change frequency. In winter, if your tank is unheated or in a cold room, you can sometimes stretch to 10-day intervals because the fish are less active. Watch your water parameters rather than following a rigid schedule if seasons change your room temperature significantly.

If you are away for more than a week, do a full water change and clean the filter before you leave. Feed your fish lightly for the days before you go, and consider a battery-powered air pump in case the power goes out. Most fish can survive two weeks without food, but they cannot survive a spike in ammonia. A clean tank at the start of your absence is your best insurance.

Frequently Asked Questions

Can I do a 50 percent water change instead of 25 percent weekly?

Yes. A larger water change removes more waste and is actually safer than a smaller one, as long as the new water is treated and at the same temperature. Some aquarists do 50 percent weekly and skip the monthly deep clean. The trade-off is that you use more water and dechlorinator, but the tank stays more stable.

What if I miss a week of water changes?

Do a water change as soon as you remember. If you missed only a few days, a normal 25 percent change should bring things back to normal. If you missed a full week or more, do a 50 percent change and test the water. If ammonia or nitrite is above zero, do another 25 percent change the next day.

Do I need to clean the substrate every week?

No. Use a siphon to remove debris from the top layer of substrate during your weekly water change, but do not dig through the whole substrate. The bacteria in the substrate help break down waste. Disturbing it too much can release trapped ammonia. A full substrate cleaning is only needed if it is clogged or smells foul.

How do I know if my filter is working well?

A working filter pulls water through smoothly and returns it to the tank without leaks. If water flow slows, the media is clogged and needs rinsing. If the filter is making noise or leaking, it may need repair or replacement. Test your water parameters—if ammonia or nitrite is above zero, the filter is not keeping up with your bioload.

Can plants reduce how often I need to clean?

Live plants consume some nitrogen waste and produce oxygen, which helps, but they do not replace water changes. A heavily planted tank may need water changes every 10 days instead of weekly, but you still need them. Plants also need maintenance—dead leaves must be removed so they do not rot and foul the water.