How to Rid a Freshwater Aquarium of Sludge

Sludge in aquariums is caused by a mix of fish waste, uneaten food and dead algae. It falls to the bottom of the tank, and since there are no currents to sweep it away, it begins to decompose in the gravel or substrate. Sludge can cause a decrease in water quality, so it's important to keep on top of removing it. You can remove sludge and do a water change at the same time using an aquarium siphon.

Things You'll Need

  • 5-gallon bucket
  • Aquarium siphon
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Instructions

    • 1

      Place a 5-gallon bucket near your aquarium. The bucket must be lower than the water level on the tank.

    • 2

      Turn off the lights on the tank. Remove the light fixture and tank lid.

    • 3

      Stick the wide end of the aquarium siphon into the tank.

    • 4

      Start the suction by sucking on the end of the hose, or by squeezing the pressure bulb on the siphon. Place the end of the hose in the bucket so the water drains into the bucket.

    • 5

      Dig the wide end of the siphon into the gravel. The suction of the water being drawn out through the hose will lift the sludge up and out while leaving the gravel.

    • 6

      Move the mouth of the siphon around by picking it up and digging it into the gravel in a different spot. Make sure you keep the mouth of the siphon underwater at all times, or you will need to restart the suction.

    • 7

      Stop the siphon temporarily by placing your thumb over the end of the hose. Have an assistant dump the bucket. As long as air bubbles don't get into the hose and the end of the hose is lower than the water level in the tank, the siphon will restart when you take your thumb off the end.

    • 8

      Keep siphoning until you have drained out approximately 15 to 20 percent of the water in the tank.

    • 9

      Replace the water with fresh water that has been treated with a dechlorination agent.