Start with a partial water change every week
The most important part of aquarium cleaning is a partial water change—removing and replacing 20 to 30 percent of the water every seven to ten days. This removes waste that has built up in the water column and keeps ammonia and nitrite levels from climbing to dangerous levels. You do not need to empty the tank or remove the fish.
Use a siphon or aquarium vacuum to pull water out while you work the tube along the gravel or substrate on the bottom. The vacuum pulls up debris, uneaten food, and fish waste as it drains. This step does two jobs at once: it removes dirty water and cleans the floor of the tank. Most aquarium vacuums have a valve you can pinch to stop the flow, so you can move around the tank without losing suction.
Replace the water you removed with fresh water at the same temperature. Cold water shocks the fish and stresses their system. Fill a bucket with tap water, let it sit for 24 hours so chlorine evaporates, or use a water conditioner to remove chlorine when ready. Some people use a thermometer to match temperatures before pouring.
Key Takeaways
- A partial water change of 20 to 30 percent every week is the single most important cleaning task and removes waste without disrupting the tank.
- Use an aquarium vacuum to clean the gravel while draining, which removes debris and fish waste in one step.
- Replace water with fresh water that has been treated for chlorine and matches the temperature of the tank.
- Clean the filter media in old tank water, never tap water, because tap water kills the beneficial bacteria that break down fish waste.
- Wipe the glass only when algae buildup blocks your view; excessive cleaning removes the protective coating on the glass.
Clean the filter in old tank water, not tap water
Your filter holds beneficial bacteria that convert ammonia (fish waste) into less toxic compounds. If you rinse the filter in tap water, the chlorine kills these bacteria and you lose months of work. Instead, use water you just removed from the tank during your water change.
Most filters have a cartridge or foam insert. Squeeze or swish it gently in the old tank water until the water runs clear. If the filter is clogged with brown sludge, it is working—that sludge is trapped waste. You are rinsing away the excess, not sterilizing it. If your filter has a motor housing or intake tube, wipe those with a cloth dampened in old tank water, but do not submerge electrical parts.
How often you clean the filter depends on the tank size and how many fish you have. A lightly stocked 20-gallon tank may need filter cleaning every two to three weeks. A heavily stocked tank or one with large fish may need it weekly. If water flow slows noticeably, the filter needs cleaning.
Wipe the glass only when algae buildup is heavy
Algae on the glass is normal and does not harm the fish, but it blocks your view. Use an algae scraper or soft cloth to wipe the inside glass. Plastic scrapers are safer than metal ones, which can scratch acrylic tanks. Wipe gently in one direction rather than scrubbing back and forth.
Do not clean the glass every week. The algae layer actually protects the glass from damage, and frequent wiping removes this protective coating. Clean the glass only when buildup is thick enough to block your view of the fish. Once every two to four weeks is usually enough.
Never use soap, vinegar, or commercial glass cleaner on the inside of the tank. These chemicals poison the water and kill fish. If you need extra cleaning power, use a soft cloth dampened only with old tank water.
Remove uneaten food and dead plants promptly
Uneaten food sinks to the bottom and rots, creating ammonia spikes that stress or kill fish. Feed only what your fish can eat in two to three minutes. If food is left after that time, you are overfeeding. Remove visible uneaten food with a net or small cup.
Dead plant leaves and stems break down in the water and foul it. Pinch off dead leaves as soon as you notice them. If a whole plant is dying, remove it entirely. Live plants actually help keep the water clean by consuming ammonia and nitrite, so they are worth keeping healthy.
Check the tank every day for debris, even on days you are not doing a water change. A quick scan takes 30 seconds and prevents problems from building up.
Clean decorations and substrate only when necessary
Rocks, driftwood, and plastic decorations collect algae and debris, but they also harbor beneficial bacteria. Do not scrub them clean every week. Instead, wipe them gently with a soft cloth during your water change if they look heavily coated. If they are only lightly covered with algae, leave them alone.
Gravel or sand substrate does not need separate cleaning if you are using an aquarium vacuum during water changes. The vacuum pulls up debris from the top layer without removing the substrate itself. If debris builds up in a corner or under a decoration, use the vacuum to spot-clean that area.
If you have a heavily planted tank or one with a lot of organic matter, you may need to vacuum more thoroughly. Watch for dead spots in the substrate—areas where the water looks cloudy or smells foul. These are pockets of decaying matter and should be vacuumed out.
Test water parameters monthly to catch problems early
A straightforward aquarium test kit measures ammonia, nitrite, and nitrate—the three compounds that build up from fish waste. You can buy a kit at any aquarium store for $20 to $40. Test strips are faster but less accurate; liquid test kits take longer but give more reliable results.
Test the water once a month in an established tank. In a new tank (less than six weeks old), test weekly because the bacteria colony is still building and ammonia can spike suddenly. If ammonia or nitrite reads above zero, increase water changes to twice a week until levels drop.
Nitrate is the end product of the nitrogen cycle and will always be present. Levels below 40 parts per million are safe for most fish. If nitrate climbs above 80, do a larger water change (40 to 50 percent) to bring it down. High nitrate means the bacteria are working but waste is accumulating faster than they can process it.
Know when to do a full tank cleaning
A full tank cleaning—removing all water, fish, and decorations—is rarely necessary in a healthy aquarium and can actually harm it by destroying the bacteria colony. Only do a full cleaning if the tank has a disease outbreak, a major algae bloom that will not respond to partial changes, or a dead fish that has been hidden and decomposed.
If you must do a full cleaning, save at least half the old water and use it to refill the tank. This preserves some of the beneficial bacteria. Remove the fish to a temporary container with some of the old water. Clean decorations in old tank water, not tap water. Rinse the gravel in old water as well. After refilling, do not add new fish for at least a week, and monitor ammonia closely.
For routine maintenance, stick to weekly partial water changes and filter cleaning. This approach keeps the tank stable and the fish healthy without the shock of a full reset.
Frequently Asked Questions
How often should I do a water change?
Every seven to ten days, changing 20 to 30 percent of the water. If the tank is heavily stocked or you have large fish that produce a lot of waste, do a water change every five to seven days. A lightly stocked tank with small fish may go ten days between changes. Watch ammonia levels with a test kit to know what works for your setup.
Can I use tap water directly in the aquarium?
Tap water contains chlorine, which kills fish and beneficial bacteria. Let tap water sit for 24 hours before adding it so chlorine evaporates, or use a water conditioner to remove chlorine when ready. Some tap water also contains heavy metals or high levels of minerals depending on your area—a water conditioner handles these too.
What if I see white or green film on the glass?
White film is usually a bacterial bloom and clears on its own within a few days. Green film is algae and can be wiped away with a soft cloth. Both are signs the tank is cycling or adjusting. Do not over-clean; just do your regular water changes and let the tank stabilize.
Is it bad to have algae in the aquarium?
Light algae growth is normal and harmless. It actually consumes some of the ammonia and nitrate in the water. Heavy algae blooms can block light from plants and make the tank look dirty, but they do not poison the fish. If algae is out of control, reduce feeding, lower the light hours to eight per day, and increase water changes.
Do I need to clean the filter every week?
Not always. Clean the filter when water flow slows noticeably or when you see brown sludge buildup. In a lightly stocked tank, this might be every three weeks. In a heavily stocked tank, it might be weekly. Always rinse the filter in old tank water, never tap water, to protect the bacteria.