The basic routine: water changes, filter maintenance, and spot cleaning
A clean aquarium stays clean through three regular tasks done on different schedules. Partial water changes (removing and replacing 20 to 30 percent of the water) happen weekly or every two weeks, depending on tank size and how many fish you have. Filter cleaning happens every two to four weeks—you rinse the filter media in old tank water (never tap water, which kills the bacteria that break down fish waste). Spot cleaning means removing visible algae, uneaten food, and dead plant matter as you notice them, usually a few times a week.
The reason for this rhythm is that fish waste and uneaten food create ammonia, which is toxic to fish. Beneficial bacteria in your filter and substrate convert ammonia to nitrite, then to nitrate, which is less harmful but still builds up over time. Water changes remove nitrate; filter cleaning keeps water flowing through the bacteria that do the conversion. Skip either one and the tank becomes toxic even if it looks clear.
Start with a gravel vacuum (a tube with a bulb or electric pump that sucks debris from the substrate while draining water). This removes the worst of the waste in one pass. Then use a net to fish out any visible food or dead leaves. Wipe the inside glass with an algae scraper or soft cloth if algae is building up. These steps take 15 to 30 minutes depending on tank size.
Key Takeaways
- Weekly or biweekly partial water changes (20 to 30 percent) remove nitrate buildup that bacteria cannot break down.
- Rinse filter media in old tank water every two to four weeks to keep water flowing without killing the bacteria that process fish waste.
- A gravel vacuum removes settled waste from the substrate and is the fastest way to clean a tank during a water change.
- Tap water contains chlorine and chloramine that kill beneficial bacteria, so always treat new water with a dechlorinator before adding it to the tank.
- Algae growth is normal and usually means light is on too long or nutrients are building up; reducing light hours and doing more frequent water changes slows it.
Water changes: how much, how often, and what water to use
The amount and frequency of water changes depend on tank size and bioload (how much waste your fish produce). A 20-gallon tank with four small fish needs a 25 percent change every week. A 55-gallon tank with the same fish might need only a 20 percent change every two weeks. A heavily stocked tank or one with large fish needs more frequent changes. The rule of thumb is: if nitrate readings stay below 40 parts per million (ppm) on a test kit, your schedule is working; if they climb above 60 ppm, change water more often or change a larger percentage.
Always treat tap water with a dechlorinator before it goes into the tank. Chlorine and chloramine (added to tap water to kill bacteria for human use) also kill the beneficial bacteria in your filter. Most dechlorinators work when ready—you add the dose to new water, wait 30 seconds, and it is safe. Some also bind heavy metals. Follow the bottle's dosing instructions; overdosing does not harm fish but is wasteful.
The water temperature should match the tank temperature within a few degrees. If your tap water is much colder or warmer than the tank, let it sit in a bucket for an hour or use a submersible heater in the bucket to bring it closer. A sudden large temperature swing stresses fish. For most tropical tanks, aim to add water that is within 2 to 3 degrees of tank temperature.
Cleaning the filter without killing the bacteria
The filter is where most of the beneficial bacteria live. If you rinse the filter media in tap water, the chlorine kills those bacteria and you lose the tank's ability to process waste. Instead, rinse the filter media in a bucket of old tank water that you removed during the water change. Squeeze or swish the media gently until the water runs clearer. You are removing trapped debris, not sterilizing the media.
How often you clean the filter depends on the filter type and how dirty it gets. Sponge filters and hang-on-back filters usually need cleaning every two to four weeks. Canister filters (larger external filters) can go four to eight weeks between cleanings because they hold more debris. If water flow slows noticeably or the filter becomes noisy, clean it sooner. A clogged filter cannot process waste effectively, so do not wait until the scheduled date if the tank needs it.
If your filter has a mechanical stage (foam, floss, or sponge that traps particles) and a biological stage (ceramic rings, lava rock, or sponge that hosts bacteria), clean only the mechanical stage during routine maintenance. Leave the biological media alone unless it is visibly clogged. This keeps the bacteria population stable.
Dealing with algae growth
Algae is a sign that light and nutrients are in balance—for algae, not for your plants and fish. Green algae on the glass is usually harmless and straightforward to scrape off. Brown algae (diatoms) often appears in new tanks and fades as the tank matures. Red or black algae (brush algae or black beard algae) is harder to remove and usually means light is on too long or phosphate levels are high.
The fastest fix is to reduce light. Most aquarium plants need 8 to 10 hours of light per day; algae thrives on 12 hours or more. If your light is on a timer, shorten it to 8 hours and see if algae slows in a week or two. If you have no plants, you can cut light to 6 to 8 hours. More frequent water changes also help by removing excess nutrients that algae feeds on.
Algae-eating fish like plecos and otocinclus catfish help but are not a complete solution—they eat some algae but not all types, and they produce waste that feeds the algae you are trying to control. A combination of shorter light hours, more frequent water changes, and manual scraping works better than relying on fish alone.
Testing water and knowing when something is wrong
A basic aquarium test kit measures ammonia, nitrite, nitrate, and pH. You do not need to test every day, but testing once a week when the tank is new (first month) and once a month after it is established tells you if your cleaning routine is working. Safe levels are: ammonia 0 ppm, nitrite 0 ppm, nitrate below 40 ppm (ideally below 20 ppm), and pH stable within your tank's normal range.
If ammonia or nitrite are above 0, the tank is not cycled or the filter is failing. Do a large water change (50 percent) when ready and clean the filter. If nitrate is climbing above 60 ppm despite your water change schedule, increase the frequency or size of changes. If pH is swinging wildly, test again to confirm and then check for decaying plants or uneaten food that might be rotting and acidifying the water.
Many fish stores offer free water testing if you bring a sample in a clean container. This is useful if you do not own a test kit yet or want a second opinion on your results.
Cleaning decorations, plants, and the glass
Decorations (rocks, driftwood, plastic plants) can be rinsed in old tank water during a water change if they are visibly dirty. Do not use soap or chemicals—they leave residue that harms fish. If a decoration has stubborn algae, soak it in a bucket of tank water for a few hours, then scrub gently with a soft brush. For live plants, remove dead or decaying leaves by hand; they rot and foul the water if left in the tank.
The aquarium glass gets algae and mineral deposits (especially on the waterline). Scrape the inside glass with a plastic or magnetic algae scraper during water changes. For the outside, use a soft cloth and plain water or a 50/50 vinegar-and-water solution. Never use window cleaner or any product that might drip into the tank.
Substrate (gravel or sand) does not need to be removed and cleaned unless it is caked with debris. The gravel vacuum during water changes removes the worst buildup. If you do a deep clean and remove all the gravel to wash it, you will lose most of the beneficial bacteria and the tank will need to recycle. Avoid this unless the substrate is truly foul.
When to call for help or do a larger intervention
If fish are gasping at the surface, the water is cloudy despite your cleaning routine, or there is a strong foul smell, something has gone wrong quickly. Do a 50 percent water change when ready, clean the filter, and test the water. These are signs of ammonia or nitrite spike, usually from a filter failure or a dead fish hidden in the tank.
If you find a dead fish, remove it right away. A decomposing fish releases ammonia and can crash the tank in hours. After removing it, do a water change and test the water. If you have multiple fish dying over days, the tank may be overstocked, the filter may be failing, or a disease may be spreading. Reduce feeding, increase water change frequency, and consider whether the tank is too small for the number or size of fish you have.
If you are unsure whether your cleaning routine is adequate or your test results are normal, a local aquarium shop can advise you. Bring a water sample and a description of your tank (size, number and type of fish, filter type, how long it has been running).
Frequently Asked Questions
How often should I do a full water change instead of a partial one?
Avoid full water changes unless the tank is severely fouled or you are treating a disease. A full change removes all the beneficial bacteria and forces the tank to recycle, which can spike ammonia and kill fish. Stick to partial changes (20 to 30 percent) weekly or biweekly. A full change is a last resort, not routine maintenance.
Can I use bottled water or distilled water instead of tap water?
Bottled water works but is expensive for regular water changes. Distilled water lacks minerals that fish need and can cause pH swings. Tap water treated with dechlorinator is the standard choice. If your tap water is very hard or has high chloramine levels, a reverse-osmosis filter or a water conditioner designed for your local water can help, but these are optional upgrades.
What if I miss a water change?
Missing one water change will not crash the tank, but nitrate will build up. Do the change as soon as you remember. If you regularly forget, set a phone reminder or move the water change to a day you are home (like Sunday morning). Consistency matters more than perfection.
Is it normal for the filter to make noise after I clean it?
A little noise is normal as water flow reestablishes. If the noise is loud or the filter is not flowing water properly, the media may not be seated correctly. Turn off the filter, reseat the media, and turn it back on. If noise persists, the impeller (the spinning part) may be worn and the filter may need replacement.
Do I need to clean the substrate if I have live plants?
Live plants help by consuming nitrate, so you may need slightly less frequent water changes. Still use a gravel vacuum during water changes to remove settled waste. The plants' roots will benefit from the nutrients in the substrate, so do not remove it entirely. A light vacuuming around plant bases is enough.