Clean your aquarium on a weekly schedule, with partial water changes every seven days and a full cleaning once a month

The most common routine is a 25 percent water change every week, which removes waste and keeps water chemistry stable without shocking your fish. A full tank cleaning—where you remove the fish temporarily, drain all water, scrub the glass and decorations, and rinse the filter—happens once a month for most home aquariums. The exact timing depends on tank size, how many fish you have, and what kind of filter you're running, but weekly partial changes are the foundation that prevents most problems.

Skipping or delaying water changes is the single biggest reason aquariums fail. Fish produce ammonia through their gills and waste; uneaten food rots; plants decay. These toxins build up invisibly until fish stop eating, develop spots or torn fins, or die suddenly. A weekly 25 percent change removes these toxins before they accumulate to dangerous levels. You don't need special equipment—a siphon hose and a bucket are enough.

Key Takeaways

  • Change 25 percent of the water every seven days to remove ammonia and waste without disrupting the bacteria that keep the tank balanced.
  • Do a full tank cleaning once a month: drain everything, scrub the glass and decorations, rinse (not replace) the filter, and refill with fresh water at the same temperature.
  • Smaller tanks under 20 gallons need more frequent changes—sometimes twice a week—because waste concentrates faster in less water.
  • If you see algae blooming, cloudy water, or a foul smell, clean more often; these are signs toxins are building up faster than your routine removes them.
  • Never replace the filter media during a cleaning; rinse it in old tank water to preserve the bacteria colony that breaks down fish waste.

Weekly Partial Water Changes: The Core of Tank Maintenance

A partial water change means removing about one-quarter of the water and replacing it with fresh water of the same temperature. Use a siphon hose or aquarium vacuum to pull water from the bottom of the tank, where waste settles. This removes decaying food, fish feces, and dissolved ammonia while leaving the beneficial bacteria in the gravel and filter untouched. The bacteria are what keep ammonia from poisoning your fish, so you never want to remove all the water at once.

The timing matters: do this every seven days, on the same day each week if possible. Set a phone reminder so you don't skip it. The water you add should be dechlorinated (let tap water sit for 24 hours, or use a dechlorinator product) and as close as possible to the temperature of the tank water—a difference of more than a few degrees stresses fish. If your tap water is very hard or very soft, you may need to adjust, but for most home aquariums, plain dechlorinated tap water works fine.

Monthly Full Tank Cleanings: When and How

Once a month, do a complete cleaning. Turn off the heater and filter, then use a net or small container to move your fish to a temporary holding tank—a large bucket or spare aquarium filled with some of the old tank water works. Drain all the water, then scrub the glass walls with an algae scraper or soft cloth. Wipe down decorations and plants (live plants can stay in the tank if you're careful). Rinse the gravel with the old tank water in a separate bucket to remove trapped waste without killing the bacteria.

The filter is the most important part: rinse the filter media in old tank water, never in tap water. Tap water chlorine kills the bacteria living in the filter, and those bacteria are doing the work that keeps your fish alive. A quick rinse in old water removes visible gunk while preserving the colony. If the filter is very clogged, rinse it gently in two or three changes of old water. Once everything is clean, refill the tank with fresh dechlorinated water at the same temperature, turn the heater and filter back on, and return your fish.

Tank Size and Stocking Affect Your Schedule

Smaller tanks need more frequent changes. A 10-gallon tank with three fish should get a 25 percent change twice a week, not once. A 5-gallon tank is difficult to maintain and may need changes every three or four days. The reason is straightforward: waste concentrates faster in less water. A 55-gallon tank with the same three fish can go longer between changes because the waste is diluted across more water.

Overstocking—keeping more fish than the tank can support—also forces you to clean more often. A good rule is one inch of fish per gallon of water (measure the fish's body length, not including the tail). If you have a 20-gallon tank, you can safely keep 20 inches of fish total. Exceeding this means more frequent water changes and a higher risk of ammonia spikes even with a good filter.

Signs Your Tank Needs Cleaning More Often

Watch for these warning signs that your routine isn't keeping up: cloudy or milky water (usually a bacterial bloom from excess waste), a foul or rotten smell, green or brown algae coating the glass or decorations, or fish gasping at the surface. Any of these means toxins are building up faster than your current schedule removes them. Increase to twice-weekly water changes when ready and check that your filter is working—a clogged filter can't process waste fast enough.

Fish behavior also signals trouble. If your fish hide constantly, stop eating, develop white spots or torn fins, or move slowly, water quality is likely the problem. Do a 50 percent water change right away, then increase your regular cleaning schedule. Most of these problems reverse within a few days if you catch them early.

Filter Maintenance Between Full Cleanings

Your filter works continuously to break down ammonia, so it needs attention even on weeks when you're not doing a full tank cleaning. Every two weeks, rinse the filter media in old tank water (save some when you do your weekly change). This removes trapped waste without killing the bacteria. If the filter is running slowly or making noise, it's probably clogged and needs rinsing sooner.

Never replace filter media unless it's falling apart. The bacteria that colonize the media are irreplaceable and take weeks to regrow. If you must replace it (because it's torn or disintegrating), do it gradually: replace one-third of the media at a time, waiting two weeks between replacements so bacteria can recolonize the new material.

Seasonal Changes and Vacation Planning

Water temperature affects how quickly waste builds up. In warmer months, bacteria and fish metabolism speed up, so you may need to increase water changes slightly. In winter, the opposite happens—you might stretch to 10 days between changes if your tank is cool. Watch your water clarity and smell; they'll tell you if the schedule needs adjusting.

If you're away for a week or more, do a full tank cleaning and a 50 percent water change before you leave. Feed your fish lightly for a few days before departure, then don't feed them while you're gone—fish can survive weeks without food, but uneaten food rots and fouls the water. Ask a trusted friend to do a 25 percent water change halfway through your absence if you'll be gone longer than two weeks.

Frequently Asked Questions

Can I do a full water change instead of partial changes?

No. A full water change removes the beneficial bacteria that break down ammonia, and it shocks fish with sudden temperature and chemistry changes. Stick to 25 percent weekly changes and one full cleaning per month. The bacteria in your gravel and filter do the real work of keeping the tank safe.

What if I miss a week of water changes?

Do a 50 percent water change as soon as you remember, then get back on schedule. Missing one week usually won't kill your fish, but the water quality will have declined. If you notice cloudiness, smell, or algae, do the large change when ready and watch for signs of stress in your fish over the next few days.

Do I need to clean the gravel every time I change water?

Not every time. Use an aquarium vacuum to clean the gravel during your weekly partial changes—this removes waste that settles on the bottom. During the monthly full cleaning, rinse the gravel more thoroughly in old tank water. Gravel that's too clean loses beneficial bacteria, so don't scrub it aggressively.

How long does a full tank cleaning take?

Plan for 30 to 45 minutes if you're moving slowly and being careful. Experienced aquarists can do it in 20 minutes. The time depends on tank size, how much algae and debris you're dealing with, and how many decorations you have to scrub. Don't rush—careful cleaning prevents mistakes that stress fish.

Should I use chemicals to clean the tank?

No. Plain water and a soft cloth or algae scraper are all you need. Soap, bleach, and commercial tank cleaners leave residue that poisons fish. If you use any cleaning tool, rinse it thoroughly in plain water before it touches the tank. For stubborn algae, a soft-bristled toothbrush and patience work better than chemicals.