The core routine: water changes, filter maintenance, and spot cleaning
A clean aquarium depends on three things done on a schedule: removing old water, cleaning the filter, and taking out visible waste. You do not need expensive equipment or chemicals—just a siphon, a bucket, and about 15 minutes per week. The filter does most of the work for you, but it clogs over time and stops working if you ignore it.
Start with a partial water change every week. Use a siphon (a tube that creates suction) to remove about 25 percent of the water from the bottom of the tank, where waste settles. This pulls out fish waste, uneaten food, and decaying plant matter without disturbing the fish. Refill with fresh water at the same temperature as the tank—cold water shocks the fish and stresses them. If your tap water is heavily chlorinated, let it sit in an open bucket for 24 hours before adding it, or use a water conditioner from a pet store.
Clean the filter every two to four weeks, depending on how many fish you have and how much they eat. The filter cartridge or media traps debris and becomes clogged. Rinse it gently in old aquarium water you just removed—never use tap water, which kills the beneficial bacteria living in the filter. Those bacteria break down fish waste into less toxic compounds, so you want to keep them alive. If you use tap water, you reset the cycle and the tank becomes toxic.
Key Takeaways
- Remove 25 percent of the water weekly using a siphon, and refill with fresh water at the same temperature to avoid stressing the fish.
- Rinse the filter cartridge every two to four weeks in old tank water, never tap water, to preserve the bacteria that keep the tank safe.
- Scrape algae from the glass and remove uneaten food and dead plant matter by hand or net as soon as you notice them.
- Test the water monthly for ammonia and nitrite if the tank is new, or if fish start acting sick or gasping at the surface.
- Overstocking the tank or overfeeding are the most common reasons tanks become dirty faster than the filter can handle.
Removing algae and debris without harming the fish
Algae grows on the glass, decorations, and plants when light and nutrients are present. A thin film is normal and harmless, but thick green or brown buildup blocks your view and can smother plants. Scrape it off the glass with a plastic scraper or old credit card—never use metal, which scratches the glass and can rust. For decorations and plants, use an old toothbrush or soft cloth to rub the algae away gently.
Remove uneaten food within a few minutes of feeding. Food that sits on the bottom rots and fouls the water. Feed only what the fish will eat in two to three minutes, once or twice a day. Many aquarium problems start with overfeeding, because excess food becomes waste that the filter cannot handle fast enough.
Dead leaves and plant matter decay and release ammonia, so pinch off dead leaves as you see them and remove them with a net. If a plant is dying, pull it out entirely rather than letting it rot in the tank. The same goes for uneaten vegetables if you feed live plants—remove them after a few hours.
Understanding ammonia, nitrite, and nitrate in your tank
Fish produce ammonia through their gills and waste. Ammonia is toxic even in small amounts. Beneficial bacteria in the filter convert ammonia into nitrite, which is also toxic. A second group of bacteria converts nitrite into nitrate, which is much less harmful and is removed during water changes. This cycle is called the nitrogen cycle, and it takes two to six weeks to establish in a new tank.
During the first month, test the water twice a week using an aquarium test kit from a pet store. You are looking for ammonia and nitrite to stay at zero. If either one rises above 0.5 parts per million (ppm), do a 25 percent water change when ready. High ammonia or nitrite means the filter is not keeping up, usually because the tank is overstocked or you are overfeeding.
Once the tank is established, test monthly or whenever fish start acting sick—gasping at the surface, hiding, or refusing food are signs of water quality problems. Nitrate will rise over time and should stay below 40 ppm. If it climbs higher, increase your water change to 30 or 40 percent weekly, or reduce the number of fish.
Preventing common problems before they start
The most common reason tanks become dirty is overstocking—too many fish for the filter to handle. A general rule is one inch of fish per gallon of water, but this varies by species and how much they eat. A 20-gallon tank with five 4-inch fish is overstocked; the same tank with three 4-inch fish and some small ones is not. If you are unsure, ask at the pet store or look up the species online.
Overfeeding is the second most common mistake. Feed once a day for small tanks, twice a day for larger ones. If food hits the bottom uneaten, you are feeding too much. Reduce the amount and watch the fish eat it all within a few minutes.
Keep the tank out of direct sunlight, which causes algae blooms. If the tank is in a sunny spot, cover it with a shade cloth or move it. Maintain a consistent temperature—most tropical fish prefer 75 to 80 degrees Fahrenheit. If the water gets too warm or too cold, the bacteria slow down and the fish become stressed.
Cleaning the glass and decorations without disrupting the tank
Scrape the inside glass weekly when you do your water change. Use a plastic scraper or magnetic algae cleaner—these have a magnet on the outside and a scraper on the inside, so you do not have to put your hand in the tank. Wipe the outside glass with a damp cloth to remove dust and fingerprints.
For decorations, rocks, and driftwood, scrub them gently with an old toothbrush while they are still in the tank, or remove them and rinse them under tap water. Do not use soap or chemicals. If algae is thick, soak the decoration in a bucket of tank water for an hour, then scrub it. Boil heavily soiled decorations for 15 minutes to sterilize them, then let them cool before returning them to the tank.
Avoid moving decorations around too often, because fish hide in them and become stressed by sudden changes. If you must rearrange, do it slowly over a few days.
When to do a deep clean and how to do it safely
A deep clean means removing the fish temporarily and cleaning the substrate (gravel or sand) thoroughly. You do not need to do this often—once or twice a year is enough if you are doing weekly water changes and filter maintenance. Deep cleans are necessary only if the substrate is caked with waste or if the tank has been neglected.
To deep clean, move the fish to a temporary container filled with tank water and an air stone or air pump to keep them oxygenated. Remove the decorations and siphon out all the water. Use a gravel vacuum—a siphon with a wide tube that stirs the substrate as it removes water—to pull out waste from the gravel. Rinse the gravel in a bucket under tap water until the water runs clear. Rinse decorations the same way.
Refill the tank slowly with fresh water at the same temperature, return the decorations, and gently return the fish. The whole process takes an hour or two. Do not clean the filter during a deep clean—wait a week, then clean it normally. Cleaning both at once removes too much beneficial bacteria and can cause an ammonia spike.
Frequently Asked Questions
How often should I change the water?
Weekly water changes of 25 percent are standard for most tanks. If the tank is overstocked or you have messy eaters, change 25 to 30 percent twice a week. If the tank is lightly stocked and well-maintained, you can stretch it to every 10 days, but weekly is safer and easier to remember.
Can I use tap water directly in the tank?
Tap water contains chlorine and sometimes chloramine, which kill fish and bacteria. Let tap water sit uncovered for 24 hours to let chlorine evaporate, or use a water conditioner from a pet store. Chloramine does not evaporate, so if your water is treated with it, you must use a conditioner.
What does it mean if my fish are gasping at the surface?
Gasping usually means low oxygen or high ammonia or nitrite. Do a 25 percent water change when ready and test the water. Check that the filter is running and the air stone is producing bubbles. If the problem continues after a water change, the tank may be overstocked or the filter may be clogged.
Do I need to remove the fish when I clean the filter?
No. Rinse the filter cartridge in old tank water while the fish are in the tank. The disturbance is minor and the fish are used to it. Removing them stresses them more than a quick filter rinse does.
How long does it take for a new tank to be safe for fish?
The nitrogen cycle takes two to six weeks, depending on temperature and whether you seed the filter with bacteria from an established tank. Test the water twice a week during this time. Once ammonia and nitrite stay at zero for a week, the tank is cycled and safe for fish.