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Regular water changes are an important part of keeping fish in the home. Doing so reduces the harmful levels of ammonia and nitrates in the water created naturally by fish. In the wild, these levels are regulated normally. However, in the enclosed environment of a freshwater aquarium, it is necessary to do water changes to ensure that the fish can enjoy a long, healthy life.



  1. 1
    Remove any lighting or lid on top of the tank to provide best access to the tank.
  2. 2
    Unplug any heating elements.
  3. 3
    Remove any artificial decorations and plants, and clean all sides of the aquarium using an algae brush, algae magnet, or algae sponge.
  4. 4
    Unplug any filters and take the filter pads, along with the artificial plants and decorations to a tub or sink.
  5. 5
    Clean the filter pads, plants, and decorations. If water has difficulty passing through the filter pad, replace it with a new one. During this time, any debris that had been stirred up will have settled into the gravel.
  6. 6
    Dip the larger end of the gravel siphon into the tank, with the hose now in the 5 gallon (18.9 L) bucket. Begin suction by either allowing the tube end to fill up with water and then moving it up and down in the water, or by sucking on the end of the hose until water begins flowing into the bucket. Push the gravel cleaner into the gravel at a 45° angle until you hit the bottom of the tank. Begin in a corner and drag the cleaner along the bottom of the tank slowly. Any debris that is heavier than the gravel should enter the cleaner and be sucked into the bucket. Continue to do this across the bottom of the tank. Concentrate on high-traffic areas where fish tend to rest or gather.
  7. 7
    Stop when you have removed 25-30% of the water in the tank. Removing too much at once can shock the fish.
  8. 8
    Take the temperature of the water in the tank, then go to the spigot and adjust the water temperature to match. Adding water of a different temperature can unnecessarily stress the fish, leaving them prone to fish diseases like Ich.
  9. 9
    With one end of the hose now in the tank, begin running water back into the aquarium. If a spigot is not available, use a smaller bucket to fill the aquarium. While the tank is filling, add the appropriate amount of de-chlorinator if you have chlorine in your water source. If using a bucket, add the de-chlorinator to the water before pouring it into the aquarium.
  10. 10
    Replace decorations and reconnect the filter.
  11. 11
    Plug in the heater and restart the filter. Hang-on-back filters (HOBs) may require a few cups of water from the tank to allow the motor to begin siphoning water again.



  • When cleaning the filter pads, only remove enough debris to allow water through the pad. There is beneficial bacteria located within the debris on the filters.
  • Small water changes are better
  • Native fish are more tolerant to temperature change than exotic or tropical fish.
  • If replacing filters, try not to replace all pads at once, or risk disrupting the beneficial bacteria colonies in the tank.


  • Note that because the filter pad is usually home to beneficial bacteria that help maintain the chemical balances in your tank. Changing a large percentage of the water while simultaneously replacing the filter pad can cause a dangerous dip in the level of beneficial bacteria present in your tank. If you have fish that are more sensitive to water quality it is suggested that you give the bacteria population time to recover before also replacing any large amount of the water in your tank as the water also contains a small amount of this beneficial bacteria.

Things You'll Need

  • 5 gallon (18.9 L) bucket
  • Access to spigot
  • Hose long enough to reach from spigot to aquarium
  • Tap water de-chlorinator
  • Gravel siphon

Article Info

Categories: Aquariums

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