The basic cleaning routine: what to do each week
Clean your aquarium in two parts: a partial water change every week, and a full deep clean every month or two. The weekly routine takes 15 to 30 minutes and keeps ammonia and nitrate from building up between deep cleans. You remove about 25 percent of the water, vacuum the gravel where waste collects, wipe the inside glass, and refill with fresh water at the same temperature as the tank.
Start by unplugging the heater and filter. Use a gravel vacuum (also called a siphon or aquarium vacuum) to pull water out while you stir the gravel—this sucks up fish waste and uneaten food that settle on the bottom. Move the vacuum slowly over the whole floor of the tank. As you work, the water level drops; when you have removed roughly one-quarter of the water, stop.
While the tank is partially empty, use a soft cloth or algae scraper to wipe the inside glass walls. Avoid harsh sponges or paper towels that can scratch acrylic tanks. Rinse the cloth in the water you just removed, not in tap water, so you do not introduce chlorine. Once the glass is clear, refill the tank slowly with fresh water that matches the temperature of the water already in the tank—use a thermometer to check, or let tap water sit for an hour first.
Key Takeaways
- A gravel vacuum removes waste from the tank floor during your weekly 25-percent water change and is the single most important tool for keeping water quality stable.
- Never remove the fish or drain the tank completely during a weekly clean; partial water changes are safer and less stressful for the fish.
- Rinse filter media in old tank water, not tap water, because chlorine in tap water kills the beneficial bacteria that break down ammonia.
- Deep cleans happen every four to eight weeks depending on tank size and fish load, and involve cleaning the filter, scrubbing decorations, and removing algae buildup.
- Temperature swings and chlorine exposure are the two biggest risks during cleaning, so always match water temperature and use dechlorinated water for refills.
How to clean the filter without losing the good bacteria
The filter is where beneficial bacteria live, and those bacteria convert ammonia (fish waste) into less toxic compounds. If you rinse the filter media in tap water, chlorine kills those bacteria and you lose months of progress. Instead, rinse the filter media in the water you just removed from the tank during your weekly change.
During a weekly clean, rinse only the filter media (the sponge, cartridge, or floss inside the filter). Squeeze it gently in a bucket of old tank water until the water runs clear. Do not scrub it hard or wring it out. Put the rinsed media back in the filter, plug the filter back in, and you are done. The filter housing itself—the plastic canister or box—stays in place and does not need cleaning every week.
During a deep clean every four to eight weeks, you can rinse the filter housing if it has visible algae or buildup, but still use old tank water. Never clean the filter media and the housing on the same day, because you want to preserve as much bacteria as possible. If the filter media is falling apart or clogged beyond rinsing, replace it with new media and keep the old media in the filter for another week so bacteria can colonize the new material.
Deep cleaning: when and how to do it
A deep clean happens every four to eight weeks, depending on how many fish you have and how much they eat. Tanks with heavy fish loads or poor filtration need deep cleans more often. Signs you need one: the water looks cloudy even after a week, algae coats the decorations, or the gravel feels slimy when you vacuum it.
For a deep clean, remove about 50 percent of the water using the gravel vacuum, working slowly over the entire floor. While the tank is half-empty, take out decorations, plants, and rocks and scrub them with a soft brush under running tap water—algae on decorations does not harm the tank, but heavy buildup can reduce water flow. Scrub the inside glass thoroughly. If there is stubborn algae on the glass, use a plastic algae scraper, not a metal one, which can scratch the tank.
Once decorations are clean and back in place, refill the tank with fresh water at the correct temperature. Clean the filter housing if needed (in old tank water), but do not replace the filter media during a deep clean unless it is visibly damaged. Plug everything back in and let the tank run for a few hours before feeding the fish heavily, because the water chemistry is still settling.
Dealing with algae without chemicals
Algae grows in every aquarium and is not a sign of failure—it is a sign that light and nutrients are present. Green algae on the glass is harmless and straightforward to remove. Brown algae (diatoms) and black algae (brush algae) are harder to scrub but still manageable without chemicals.
For green algae on the glass, use a plastic algae scraper or a soft cloth during your weekly clean. For algae on decorations and gravel, the gravel vacuum and scrubbing during deep cleans removes most of it. If algae is thick and stubborn, reduce the light your tank receives—most aquariums do not need more than 8 to 10 hours of light per day, and less light slows algae growth without harming plants or fish.
Black brush algae is tougher and does not respond to scrubbing. It usually means the tank is overstocked or the filter is not strong enough. Improving water flow and doing more frequent water changes will slow its growth. If you want to speed things up, add an algae-eating fish like a pleco or otocinclus, but only if your tank is large enough for that species. Never use algae-killing chemicals in a tank with fish unless a veterinarian recommends it, because most algaecides harm fish and the beneficial bacteria.
Tools you need and tools you do not
A gravel vacuum is essential—it is the one tool that does the most work. A basic siphon model costs $15 to $30 and lasts for years. An electric gravel vacuum costs more but requires less physical effort. You also need a soft cloth or sponge for wiping glass, a plastic algae scraper for stubborn spots, and a thermometer to match water temperature during refills.
A bucket dedicated to the aquarium is useful for holding old water while you rinse the filter. Do not use a bucket that has held soap, chemicals, or food. A net for moving fish is optional—most of the time you do not need to remove fish during cleaning, and netting them causes stress.
You do not need a water test kit for routine cleaning, though one is useful if you are troubleshooting cloudy water or fish behavior problems. You do not need special aquarium cleaning chemicals; old tank water and a soft brush handle almost every cleaning job. Avoid products labeled "aquarium safe" unless a fish veterinarian recommends them, because many are unnecessary and some harm the bacteria that keep the water safe.
Common mistakes that harm fish during cleaning
The biggest mistake is removing all the water and scrubbing the tank completely clean. This kills the beneficial bacteria and leaves the fish in water with no biological filtration. The ammonia from fish waste then spikes and can poison the fish within days. Partial water changes preserve the bacteria and are safer.
The second mistake is using tap water without letting it sit or treating it. Chlorine in tap water kills bacteria and can irritate fish gills. If your tap water is chlorinated, let it sit uncovered for 24 hours before adding it to the tank, or use a dechlorinator product. Many dechlorinators also bind heavy metals and cost a few dollars per bottle.
Temperature shock is the third common problem. If you add water that is much colder or warmer than the tank, fish can go into shock and stop eating or die. Always match the temperature of refill water to the tank water, or add new water very slowly so the temperature changes gradually.
Finally, do not clean the filter and do a large water change on the same day. Both remove bacteria from the system, and doing both at once can crash the nitrogen cycle. If you need to do both, do the water change first and wait a week before cleaning the filter.
What to do if the water turns cloudy after cleaning
Cloudy water after a cleaning usually means a bacterial bloom—beneficial bacteria are multiplying because organic matter was stirred up or because the filter was cleaned too aggressively. The water will clear on its own in three to seven days as the bacteria settle and the filter catches particles. Do not do another water change or clean the filter again, because that will make it worse.
If the water stays cloudy for more than a week, the problem is usually overfeeding or a filter that is too weak for the tank size. Feed the fish less and do a 25-percent water change every other day until the water clears. If you have a filter that is undersized for your tank, consider upgrading to a stronger one.
If the water turns brown or yellow after cleaning, tannins from decorations or substrate are leaching out. This is harmless to fish and will fade over time. You can speed it up by doing larger water changes, but it is not necessary.
Frequently Asked Questions
Can I use tap water straight from the faucet?
Not if your tap water is chlorinated. Chlorine kills the beneficial bacteria in your filter. Let tap water sit uncovered for 24 hours before adding it, or use a dechlorinator product. If you are unsure whether your water is chlorinated, contact your local water utility—they can tell you.
How often should I change the filter cartridge?
Replace the filter media only when it falls apart, clogs so badly that rinsing does not help, or stops letting water flow through. For most tanks, that is every three to six months. Rinsing the media in old tank water every week extends its life and keeps the bacteria alive.
Do I need to remove the fish during cleaning?
No. Removing fish stresses them and increases the risk of injury. Leave them in the tank during weekly and deep cleans. The only time to remove fish is if you are treating the tank for disease or if a decoration is so large that you cannot clean around it safely.
What if my tank has live plants?
Live plants benefit from the same cleaning routine as fish-only tanks. During water changes, trim dead leaves and remove algae from plant stems gently. Do not use algaecides around plants unless the product is labeled safe for planted tanks. Plants actually help reduce algae by competing for nutrients, so they are worth keeping.
How do I know if I am cleaning too much or not enough?
If the water stays clear and the fish eat normally, your cleaning schedule is working. If the water gets cloudy or smells bad between cleanings, you are not cleaning enough—increase to twice-weekly water changes. If the fish stop eating or hide after cleaning, you may be cleaning too aggressively or using water that is too cold.