Start with a partial water change every week

The fastest way to keep your aquarium clean is to remove about 25 percent of the water once a week and replace it with fresh water. This removes waste that has settled on the bottom and dissolved chemicals that build up over time. You do not need to empty the tank or move your fish—just siphon out the old water and pour in new water that matches the temperature of what remains in the tank.

Use a gravel vacuum (also called a siphon) to pull water from the bottom while you work. Place one end of the tube into the tank near the gravel, squeeze the bulb at the top a few times to start the flow, and let gravity pull the water into a bucket below the tank. Move the tube slowly across the bottom to pick up fish waste and uneaten food. This single step removes most of the debris that would otherwise cloud the water or harm your fish.

Let the water you remove sit for 24 hours before you pour it down the drain if you want to use it for houseplants—it is rich in nitrogen from fish waste. The fresh water you add should be at or within 2 degrees of the tank temperature, or a sudden change can stress your fish.

Key Takeaways

  • A weekly 25 percent water change with a gravel vacuum removes most waste without disrupting your tank or fish.
  • Clean the filter cartridge or media every two to four weeks by rinsing it in old tank water, never tap water, to preserve the bacteria that keep the tank healthy.
  • Wipe the inside glass with a soft algae pad or cloth, and scrape stubborn algae with a plastic scraper—never use metal or abrasive materials.
  • Test water parameters (ammonia, nitrite, nitrate) monthly with a kit to catch problems before they harm your fish.
  • Do a full tank cleaning only once or twice a year; frequent complete cleanings destroy the beneficial bacteria that break down waste.

Clean the filter every two to four weeks

The filter is where beneficial bacteria live—bacteria that convert fish waste into less harmful compounds. If you do not clean it, it clogs and stops working. If you clean it wrong, you kill the bacteria and have to start over. The solution is to rinse the filter media in old tank water that you removed during your water change, never in tap water.

Most filters have a cartridge or sponge that you pull out and rinse gently under running water from your bucket of old tank water. Squeeze it a few times to release trapped debris, but do not scrub it hard or wring it out. If the cartridge is falling apart or has holes, replace it. If it is still intact, put it back in the filter. The whole process takes five minutes and keeps the filter working without destroying the bacteria colony.

If your filter has a motor or intake tube, wipe those parts with a soft cloth while the cartridge is out. Check that the intake is not blocked by algae or debris. Once a year, replace the activated carbon insert if your filter has one—carbon absorbs chemicals and eventually becomes full.

Scrape algae from the glass and decorations

Algae grows on the glass, rocks, and plants in every aquarium. A small amount is normal and harmless, but thick green or brown coatings block your view and can smother plants. Wipe the inside glass with a soft algae pad (a felt or foam pad on a handle) or a clean cloth. Move it in circles and do not press hard—you are removing a thin layer, not scrubbing.

For stubborn spots, use a plastic scraper with a flat edge. Hold it at a shallow angle and push gently. Never use a metal scraper, steel wool, or anything abrasive—these scratch the glass and can damage the sealant at the seams. If you have acrylic instead of glass, a soft cloth is your only safe option; plastic scratches easily.

Algae on rocks and decorations can be left alone unless it is so thick it looks unnatural. If you want to remove it, scrub the object with a soft brush under running water outside the tank. Do not use soap or chemicals. Algae on live plants is usually a sign that light or nutrients are out of balance, so focus on that rather than scraping the leaves.

Test water chemistry monthly

Water that looks clean can still be toxic to fish. Test for ammonia, nitrite, and nitrate once a month using a liquid test kit (more accurate than strips). Ammonia and nitrite should always be zero. Nitrate should be below 40 parts per million, though some fish tolerate higher levels. If ammonia or nitrite is above zero, do a 50 percent water change when ready and check that your filter is running and clean.

High nitrate means waste is building up faster than your water changes can remove it. Increase to a 50 percent change weekly, or add live plants to the tank—they consume nitrate as fertilizer. Test the pH (acidity) once a month too. Most fish do well between 6.5 and 7.5, but the exact number depends on what species you keep. If pH is drifting, it usually means you need more frequent water changes.

Keep a straightforward log of your test results on a calendar or notebook. You will spot trends—for example, nitrate climbing every month tells you that you need bigger or more frequent water changes. A kit costs $20 to $30 and lasts for hundreds of tests.

Do a full tank cleaning only once or twice a year

A complete drain-and-scrub is tempting when the tank looks dirty, but it is the fastest way to crash a tank. Draining everything kills the bacteria in the gravel and filter, and refilling with fresh water means ammonia and nitrite spike within days. Fish can die before the bacteria rebuild. Save a full cleaning for once or twice a year, usually in spring and fall.

When you do a full clean, remove your fish to a temporary container with some of their old tank water. Drain the tank completely and scrub the glass and gravel with a brush and plain water. Rinse all decorations. Refill with fresh water at the right temperature, then return the fish. Do a 50 percent water change a week later to help the bacteria recover faster. For the next month, test water every few days and do 25 percent changes twice a week until ammonia and nitrite stay at zero.

Clean the tank exterior and equipment

Dust and algae build up on the outside of the glass and on the hood or light. Wipe the exterior glass with a dry cloth once a week. If it is smudged, use a cloth barely dampened with water—never spray cleaner near the tank, as fumes can harm fish. Wipe the hood and light with a dry cloth too.

Check the air pump intake (if you have one) and make sure it is not blocked. If the tubing is cloudy or has algae inside, replace it—cloudy tubing reduces air flow. Heater cords and thermometers can be wiped clean with a damp cloth. If your heater is covered in mineral deposits, soak it in white vinegar for an hour, then rinse and dry it before putting it back.

Prevent common cleaning mistakes

The most common mistake is cleaning too often or too thoroughly. A tank that looks a little cloudy or has some algae is usually healthier than one that has been scrubbed clean, because the bacteria are still there. Resist the urge to drain and refill more than once a week unless water tests show a problem.

Never use soap, bleach, or aquarium-specific "cleaners" inside the tank. These kill fish and bacteria. If something needs to be disinfected, soak it in a 10 percent bleach solution (one part bleach to nine parts water) for 15 minutes, then rinse it thoroughly under running water for at least two minutes before it goes back in the tank. Better yet, just rinse with plain water—most algae and debris rinse away.

Do not change the filter cartridge and do a full tank cleaning in the same week. You need the bacteria in at least one place (the gravel or the filter) to survive the disruption. If the cartridge is falling apart, replace it, do your normal water change, and skip the full clean that week.

Frequently Asked Questions

How often should I change the water?

Once a week at 25 percent is the standard for most tanks. If you have more fish than the tank is designed for, or if water tests show nitrate climbing fast, change 50 percent weekly instead. Tanks with live plants can sometimes go longer because plants consume waste, but weekly changes are still the safest routine.

Can I use tap water straight from the faucet?

Tap water is usually safe for fish, but it varies by location. Some tap water contains chlorine or chloramine, which kill fish and bacteria. If your water smells like a swimming pool, treat it with a dechlorinator before adding it to the tank. These are inexpensive drops or powders sold at any aquarium store. Let treated water sit for 24 hours before use if possible, or add it slowly while the filter is running.

What if I see white cloudy water after a water change?

Cloudy water usually means bacteria are blooming because the water chemistry changed. It clears on its own in a few days. Do not do another water change—that will make it worse. Just run the filter and wait. If it does not clear in a week, test for ammonia and nitrite; if both are zero, the cloudiness is harmless.

Is it bad to clean the gravel?

Cleaning the gravel with a vacuum during your weekly water change is good. Removing the gravel entirely and washing it is bad because it destroys the bacteria living in it. Use the gravel vacuum to suck up debris from the top layer only, without digging deep or stirring up the bottom.

How do I know if my filter is working?

You should see water flowing out of the filter outlet into the tank. If the flow is weak or stopped, the cartridge is clogged. Clean it by rinsing in old tank water. If flow is still weak after cleaning, the motor may be failing and the filter may need to be replaced.