Start with a partial water change, not a full drain

The most common mistake is emptying the entire tank and scrubbing it clean. This removes the beneficial bacteria living in your gravel and filter—the same bacteria that keep ammonia and nitrite from poisoning your fish. Instead, remove about 25 to 30 percent of the water each time you clean, which is usually once a week for a standard tank.

Use a siphon or aquarium vacuum to pull water from the bottom of the tank where waste collects. A siphon is a straightforward tube you fill by mouth or with a hand pump, then let gravity do the work into a bucket. An aquarium vacuum is a wider tube with a bulb at the top that you pump to start the flow. Both remove debris while you're draining, saving you a second step.

Key Takeaways

  • Remove 25 to 30 percent of the water weekly using a siphon or vacuum, never drain the entire tank at once.
  • Clean the glass with a soft algae pad or cloth, and scrape stubborn spots with a plastic scraper—never use metal or abrasive materials.
  • Rinse the filter media in old tank water you've just removed, not in tap water, to preserve the bacteria that keep your tank stable.
  • Replace the drained water with fresh water at the same temperature, added slowly to avoid shocking your fish.
  • Clean decorations and plants only when algae buildup is visible, and use only water and a soft brush.

Clean the glass without damaging it

Algae grows on the inside glass of every aquarium. A soft algae pad (the kind made of felt or foam) removes it without scratching. Wet the pad and rub in circular motions on the glass. For stubborn spots, use a plastic scraper held at a low angle—push rather than dig. Never use metal scrapers, scouring pads, or any abrasive cleaner, which will scratch acrylic tanks and leave residue that harms fish.

The outside glass can be cleaned with a standard glass cleaner, but spray it on a cloth first, never directly on the tank. Keep the cleaner away from the water line and any seams. Wipe dry with a lint-free cloth to prevent streaks.

Rinse the filter in old tank water

Your filter cartridge or media traps waste, but it also houses the bacteria colony that processes ammonia. Rinsing it in tap water kills those bacteria. Instead, rinse it in the water you just removed from the tank—the bucket you filled during the water change. Squeeze or swish the filter gently in that old water until it runs clear, then put it back in the filter.

If your filter has a mechanical pre-filter (a foam pad that catches large debris), rinse that more aggressively. The biological media underneath—whether it's cartridges, sponges, or beads—should be rinsed gently. Replace the mechanical pre-filter every month or two, but keep the biological media for at least a year unless it falls apart.

Add fresh water at the right temperature

Fill a separate bucket with tap water and let it sit for 15 to 30 minutes so chlorine can evaporate. If your tap water is heavily chlorinated, use a water conditioner (a few drops per gallon) instead. Check the temperature with a thermometer—it should match the tank temperature within 2 degrees Fahrenheit. Cold water shocks fish and can trigger disease.

Pour the water slowly into the tank, or pour it onto a plate or rock to break the flow and avoid stirring up gravel. This takes longer but prevents your fish from being tossed around and keeps debris settled. Top up the tank to its original level.

Clean decorations and plants only when needed

Decorations and live plants don't need cleaning every week. Algae on them is normal and actually feeds some fish. Only clean them when algae buildup is so thick it blocks light or looks unsightly. Use a soft brush and old tank water—the same water from your change bucket. Scrub gently and rinse in that water before putting the decoration back.

For live plants, pick off dead leaves by hand and trim stems with scissors if they're overgrown. Don't soak plants in anything but tank water. Artificial plants can be rinsed under tap water if needed, but natural plants should stay in tank water only.

Clean the substrate only during major cleanings

Gravel and sand are home to beneficial bacteria and to the microorganisms that fish eat. Vacuuming the top layer during your weekly water change is fine, but don't dig deep or stir up the substrate. Every two to three months, you can do a deeper clean by removing decorations and vacuuming more thoroughly, but this is optional if your tank looks clean.

Never replace the substrate entirely unless it's visibly falling apart or your tank has had a disease outbreak. If you do replace it, keep some of the old substrate and mix it with the new to preserve your bacterial colony. Rinse new gravel in a bucket under tap water until the water runs clear before adding it to the tank.

Maintain a cleaning schedule

A standard 20-gallon tank with a few fish needs a 25 to 30 percent water change and glass cleaning once a week. Smaller tanks (10 gallons or less) may need cleaning twice a week because waste builds up faster. Heavily stocked tanks or tanks with large fish need more frequent changes. Lightly stocked tanks with good filtration might go two weeks between changes.

The easiest way to stay on track is to clean on the same day each week. Set a phone reminder if you need one. A clean tank keeps fish healthy and makes the tank look better, but the goal is stability, not perfection. Consistent partial changes matter far more than occasional deep cleans.

Frequently Asked Questions

Can I use tap water straight from the faucet?

Tap water contains chlorine that harms fish. Let it sit 15 to 30 minutes before adding it to the tank, or use a water conditioner to remove chlorine when ready. If your tap water is very hard or very soft, you may need to adjust it, but for most fish a straightforward dechlorination is enough.

How often should I replace the filter cartridge?

Replace the mechanical pre-filter (the foam that catches debris) every month or two, or when it looks clogged. Keep the biological media—cartridges, sponges, or beads—for at least a year. Replace it only when it falls apart or your tank develops ammonia or nitrite problems despite regular cleaning.

What if my tank has a lot of algae on the glass?

Heavy algae usually means too much light or too many nutrients. Clean the glass with an algae pad during your regular water change, then reduce light to 8 to 10 hours a day and do slightly larger water changes (30 to 40 percent) for a few weeks. Algae-eating fish like plecos or otocinclus can help, but they work best alongside these changes.

Is it okay to clean everything at once?

No. Cleaning the filter, glass, and decorations all in one session removes too much of your bacterial colony at once. Spread it out: clean the glass and do a water change every week, rinse the filter during that same change, and clean decorations only when you see heavy algae buildup.

What should I do if my fish look stressed after cleaning?

Stress usually comes from temperature shock or sudden water changes. Make sure new water is within 2 degrees of tank temperature and add it slowly. If you cleaned the filter in tap water instead of old tank water, the ammonia may spike in a few days—watch for gasping or lethargy and do a large water change (50 percent) if that happens.