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Aquarium guides/How to clean a fish tank

How to clean a fish tank: a water-change checklist

For a routine clean, unplug the heater and filter first. If the water will drop below the heater, or you will lift it out, let it cool before you start: Aqueon says at least 30 minutes. Scrape the glass, then siphon out 10 to 25 percent of the water while vacuuming the gravel. Refill with dechlorinated water close to the tank’s temperature and restart the filter the way its manual says, priming a canister if it needs it. Plug the heater back in only after it has been under water again for its maker’s wait, another 30 minutes for Aqueon’s. Check for leaks before you walk away.

Cleaning inside a tank by hand
Shown: cleaning inside a tank by hand. Photo: U.S. Fish and Wildlife Service, Public domain, via Wikimedia Commons

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The steps in pictures

  1. Unplug first. Right looks like this: Heater and filter unplugged; if the water will drop below the heater, let it cool 30 minutes first.

  2. Scrape the glass. Right looks like this: Glass scraped before you siphon, so the loosened algae leave with the water.

  3. Siphon and vacuum. Right looks like this: 10 to 25 percent out, the siphon working through the gravel as it goes.

  4. Refill to temperature. Right looks like this: Dechlorinated water close to the tank’s temperature, poured gently back in.

  5. Restart and check. Right looks like this: Filter running the way its manual says, heater plugged in after its wait, and no leaks.

What to clean, and how much water to change

Decide what today’s clean covers: a water change, the gravel, the glass, the filter, or all of them. Cleaning the filter on a different day from a big gravel clean spares the bacteria that live in both; when the filter’s turn comes, rinse its sponges in the tank water you have just siphoned out. Start with 10 to 25 percent every week or two, then adjust to how many fish you keep and what your tests read: change more when nitrate climbs or ammonia shows at all.

The heater waits are Aqueon’s: at least 30 minutes to cool before a heater comes out of the water, and at least 30 minutes back in it before you plug it in. Its Pro heater manual also says never to leave a heater plugged in out of water. Other makers give their own times, so check the manual for yours. The water-change calculator turns your percentage into gallons and bucket trips.

Before you start

  • Keep a bucket for the aquarium only: soap left in a household bucket harms fish. Have the siphon or gravel vacuum ready and a clear path to the sink or drain.
  • Prepare the new water: dechlorinate it at the dose on your conditioner’s bottle and bring it close to the tank’s temperature.
  • Unplug the heater and filter before the water level drops, and let the heater cool first if it will be out of the water.
  • Put a towel down for drips.

Conditioners differ in what they treat and how much to use, so follow the bottle you own. Compare water conditioners

Cleaning the filter and heater

Keep plugs and sockets dry and leave the heater unplugged while you work. Clean the filter the way its manual describes: rinse sponges and pads in the tank water you siphoned out, never under the tap, because chlorine kills the bacteria that keep the water safe. If the flow had dropped, take out the impeller and rinse it and its well. Replace only what is worn out or what the manual says to replace; biological media such as ceramic rings and sponges only needs replacing when it falls apart, and throwing it out sets the cycle back. Filter maintenance by model

Refill and restart

Refill to the filter’s water line, pouring onto a plate or your hand so the gravel stays put. Prime and restart the filter the way its manual says, then watch it for a minute: steady flow and no drips at the lid, hoses or valves. Plug the heater back in once it has been under water for its maker’s wait.

If the flow does not come back, the filter makes a new noise or anything drips, stop and use the troubleshooting checks rather than restarting it again and again. A note of what you cleaned and what your tests read makes the next change easier to judge.

Cleaning isn’t disinfecting

A routine clean keeps the tank healthy, but it does not kill disease organisms. Nets, siphons and decor moved between tanks can carry them, so keep separate tools for a quarantine or sick-fish tank. To disinfect used equipment or after an outbreak, UF/IFAS describes methods that depend on the material and the disease, and some disinfectants damage acrylic, rubber seals or pumps, so ask the maker what its parts can take. Checking used equipment

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