How to Change the Substrate in a Marine Fish Tank

The substrate in a fish tank, also known as filter bed, is a level of gravel or sand which fulfills a biological task and hosts beneficial bacteria. The substrate should be periodically changed or vacuumed to provide a clean environment for your fish. When changing the substrate be mindful of the beneficial bacteria that exists in the substrate. These bacteria reduce the amount of poisonous substances found in the fish waste and by-products and preserve the chemical balance of the tank.

Things You'll Need

  • Plastic hose
  • Buckets
  • Fine-weave nets
  • Sieve
  • Towel
  • Bacterial additives
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Instructions

  1. Change Gravel Substrate

    • 1

      Unplug the heaters and filters of your tank so you won't get electrocuted.

    • 2

      Remove 20 to 30 percent of the amount of the water in your fish tank. Place a flexible plastic hose into the tank and use your mouth to suck on the other end. Once the water starts coming out, direct the hose toward a bucket. Collect the water in this bucket. Select the size of your buckets according to the size of your tank. If the capacity of your tank is 20 gallons, use a 10-gallon bucket.

    • 3

      Remove 20 to 30 percent of the amount of the water in your fish tank. Place a flexible plastic hose into the tank and use your mouth to suck on the other end. Once the water starts coming out direct the hose toward a bucket. Collect the water in this bucket. Select the size of your buckets according to the size of your tank. If the capacity of your tank is 20 gallons, use a 5- or 10-gallon bucket.

    • 4

      Net the fish and place them in the bucket.

    • 5

      Remove any corals or rocks from the tank and place them in a bucket or a clean surface.

    • 6

      Use a fine-weave (0.04-inch mesh) net to extract the gravel from the tank. Remove only up to half of the amount of substrate material at once to preserve the beneficial bacteria in the substrate. Place the extracted gravel in a bucket and safely dispose of it after you finish changing the substrate.

    • 7

      Rinse the gravel you use as a fresh substrate. The amount of fresh substrate should equal the amount of dirt extracted substrate. Place the fresh material in a bucket and pour tap water over it. Remove the water. As an alternative, sift the gravel to remove dust and other debris.

    • 8

      Load the fresh substrate material all at once.

    • 9

      Place the fish back in the tank together with the water you extracted.

    Change Sand Substrate

    • 10

      Soak the sand you intend to use as a substrate for 48 hours prior to placing it inside the tank. When changing the sand substrate, you need to place the sand in an empty tank and avoid pouring the sand into water.

    • 11

      Remove water from your tank to fill a bucket of water.

    • 12

      Net the fish and place them in the bucket.

    • 13

      Drain the tank completely and rinse it with tap water. Keep the water in buckets while you change the substrate.

    • 14

      Remove the dirty substrate and wipe the interior of the tank with a clean towel. Preserve half of the old substrate, which contains the friendly bacteria necessary to break down the harmful waste materials in the tank.

    • 15

      Mix the old sand with the soaked replacement sand.

    • 16

      Place the sand into the tank and slowly pour each bucket into the tank, finishing with the bucket containing the fish.