Start with a weekly partial water change

The single most effective way to keep your aquarium clean is to replace 25 to 30 percent of the water every week. This removes waste that has dissolved in the water—ammonia, nitrite, and nitrate—without disrupting the bacteria colony that keeps your tank stable. A partial change is safer than draining and refilling completely, which can shock your fish and kill the beneficial bacteria living in your filter and substrate.

Use a siphon gravel vacuum to do this job. Push the tube into the gravel as you siphon; this pulls out fish waste and uneaten food that settle on the bottom. Start the siphon by filling the tube with water from the tank, then let gravity do the work into a bucket. Most aquariums lose 25 to 30 percent of their water in 10 to 15 minutes this way. Replace what you removed with fresh water at the same temperature—cold water shocks fish and can cause illness.

Key Takeaways

  • Change 25 to 30 percent of your aquarium water every week using a siphon gravel vacuum to remove waste from the bottom.
  • Replace your filter media every two to four weeks, or when water flow slows noticeably, to keep ammonia and waste from building up.
  • Feed your fish only what they can eat in two to three minutes once or twice daily, because uneaten food rots and fouls the water.
  • Test ammonia and nitrite levels with a liquid test kit every two weeks; levels above zero mean your filter is not keeping up.
  • Clean the glass and decorations monthly with a soft algae scraper or cloth, but avoid harsh chemicals that can poison your fish.

Replace your filter media on a schedule

Your filter traps solid waste and houses the bacteria that convert ammonia into less toxic compounds. Over time, the filter media clogs with debris and the bacteria layer thickens, slowing water flow. When you notice the water moving through the filter more slowly than usual, or every two to four weeks for a standard tank, rinse the filter media in old aquarium water you removed during your water change.

Rinse in the old tank water, not tap water—tap water kills the beneficial bacteria you need. Squeeze the media gently until the water runs clearer, then put it back. If the media is torn, falling apart, or clogged beyond rinsing, replace it with new media of the same type. Check your filter's instruction manual for the correct replacement part; using the wrong size or type reduces how well it cleans.

Feed the right amount and remove uneaten food

Overfeeding is the most common cause of dirty aquariums. Fish waste and uneaten food both produce ammonia, which builds up and stresses your fish. Feed once or twice daily, giving only what your fish can eat in two to three minutes. Most home aquariums are overfed; your fish will not starve on less food than you think they need.

Watch your fish eat. If food hits the bottom and sits there, you fed too much. Remove uneaten food with a small net within a few minutes. Food that decays on the substrate produces ammonia faster than fish waste alone, and it clouds the water. If you have bottom-feeding fish like plecos or corydoras catfish, they will eat some fallen food, but they cannot eat all of it—you still need to remove excess.

Test water chemistry every two weeks

A liquid test kit measures ammonia, nitrite, nitrate, and pH. These numbers tell you whether your filter is working and whether your tank is safe for fish. Ammonia and nitrite should both read zero; if either is above zero, your filter is not keeping up and you need to do a water change when ready and check your feeding amount.

Nitrate will always be present—it is the end product of the nitrogen cycle and builds up over time. In most tanks, nitrate reaches 20 to 40 parts per million between water changes. If it climbs above 80, increase your weekly water change to 40 or 50 percent. Test every two weeks at first; once your tank is stable, you can test monthly. A liquid kit costs $20 to $35 and lasts for hundreds of tests, making it far cheaper than test strips.

Clean the glass and decorations monthly

Algae grows on the glass, decorations, and plants in every aquarium. A thin layer is normal and harmless, but thick algae blocks light and makes the tank look neglected. Use a soft algae scraper or a cloth to wipe the inside glass once a month. Plastic scrapers work on acrylic tanks; metal scrapers work on glass but can scratch if you press too hard.

Wipe decorations and plants with your hand or a soft brush to remove algae buildup. Do this during your weekly water change so loose algae gets siphoned out. Never use soap, bleach, or window cleaner inside the tank—these poison fish. If algae is thick and stubborn, soak the decoration in a bucket of water for an hour, then scrub with a soft brush. Algae growth usually means either too much light (reduce tank lighting to 8 to 10 hours daily) or too many nutrients (check your feeding and filter maintenance).

Maintain your filter and air pump

Your filter's motor and intake tube collect debris over time. Once a month, rinse the intake tube and the outside of the filter housing under tap water to remove dust and algae. Check that water is flowing smoothly into the filter and out into the tank. If the intake is clogged, water cannot circulate and waste builds up.

If you have an air pump powering an air stone or decoration, clean the air stone every month by soaking it in hot water for 10 minutes to dissolve mineral buildup. A clogged air stone produces fewer bubbles and reduces oxygen in the water. Replace the air pump tubing every six months or if it becomes cloudy or brittle—old tubing cracks and leaks.

Avoid common mistakes that cloud your tank

New tanks often go cloudy after a few days because bacteria are multiplying rapidly—this is normal and clears on its own in a week or two without any action. Do not do large water changes or add chemicals; let the cycle finish. If your tank stays cloudy after two weeks, test ammonia and nitrite; if both are zero, the cloudiness is likely algae or mineral buildup, not bacteria.

Never clean your filter with tap water or replace all the media at once—both kill the bacteria that keep ammonia under control. Never use gravel cleaner, algae killer, or other additives unless you have tested your water and confirmed you need them; most problems come from overfeeding or infrequent water changes, not from missing chemicals. Never do a complete water change unless your fish are sick or the tank has a serious problem; partial changes are safer and more effective.

Frequently Asked Questions

How often should I clean my aquarium filter?

Rinse the filter media every two to four weeks in old tank water, or sooner if water flow slows noticeably. Do not replace the media unless it is torn or so clogged that rinsing does not restore flow. Rinsing in old tank water preserves the bacteria; rinsing in tap water kills it and can cause ammonia spikes.

Can I use tap water for water changes?

Yes, but let it sit for 24 hours first if your tap water is heavily chlorinated, or use a dechlorinator product. Most municipal tap water is safe for fish after sitting overnight. If your tap water is very hard or has high pH, you may need to treat it, but for most home aquariums, tap water works fine after a day of sitting.

What does cloudy water mean?

New tanks often turn cloudy after a few days as bacteria multiply—this clears on its own in one to two weeks. Established tanks that turn cloudy usually have algae or mineral buildup, not bacteria. Test ammonia and nitrite; if both are zero, do a partial water change and reduce lighting to 8 hours daily. If ammonia or nitrite is above zero, do a large water change when ready and check your feeding.

Do I need to clean the gravel completely?

No. Gravel contains beneficial bacteria and should not be removed or replaced unless it is visibly foul or your fish are sick. Use a siphon vacuum weekly to remove waste from the surface without disturbing the gravel underneath. Gravel stays in place and keeps working.

How do I know if my filter is working?

Water should flow smoothly into the filter intake and out into the tank. Test ammonia and nitrite every two weeks; both should read zero. If either reads above zero, your filter is not keeping up—increase water changes to 40 to 50 percent weekly and check that the filter media is not clogged. If the intake tube is blocked or water barely flows, clean or replace the media.