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How to Baffle a Fish Filter for a Betta

By Chris Miksen

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Despite her aggression toward most fish, the betta prefers a relaxing tank environment. Filters that blast water into the tank and create a fast current are troublesome to the flowing-finned fish. If you can't adjust your filter's outflow strength enough to make a difference, you can create a homemade baffle that stymies the fast-moving water.

Step 1

Unplug your betta's filter and remove it from the tank. While it's possible to baffle the strong water flow by leaving the filter in place, you'll make things easier on yourself by removing it briefly.

Step 2

Remove the label from a water bottle, rinse the inside with hot water and clean the outside, rubbing your fingers along the sticky adhesive left behind from the label to ensure it washes away. Don't use soap or chemicals to clean the bottle, as traces of their residue can be toxic to your little swimmer.

Step 3

Position the water bottle horizontally across the filter so that the center portion of the bottle -- typically where the label wraps around -- spans the outflow. The outflow is where the water flows out of the filter and returns to your tank.

Step 4

Use a marker to draw two lines on the bottle indicating where it lines up with both sides of the outflow. Cut along the inside of those two lines around the cylinder so you're left with an open tube. Make sure you cut along the inside of the lines; you don't want any marker residue left on the baffle.

Step 5

Cut the tube in half lengthwise. Picture this: you have a tube that's open on both sides. Pretend it's standing so that one open side is the bottom and one open side is the top. Make one cut from the top opening to the bottom opening. After completing this step, you should have one intact piece that opens up flat, not two separate halves.

Step 6

Affix one end of the tube between the filter media and the outflow. Immediately behind your filter outflow sits your filter media. You'll need to remove or open your filter's cover to access this area. Between the media and the outflow is a small amount of space where you can slide one end of the tube down into. The other end of the tube naturally curls in front of the outflow. When the water flows out of the filter, it pushes against your newly made baffle and gets redirected downward or back toward the wall of your betta's tank, leaving her with greatly reduced surface agitation. Alternatively, you can wrap one end of the plastic tube below the bottom lip of the outflow and tape the other end of the tube to the top cover of the filter.

Step 7

Reattach the filter. If you do not have a self-priming filter, fill up your filter's reservoir by pouring in water from your betta's tank. Plug in the filter and continue pouring in water until it begins filtering normally.

Items you will need

  • 16.9-ounce or similar-size disposable plastic water bottle
  • Scissors
  • Marker
  • Tape


  • 💡 If you find that the water flow displaces the baffle, tape it to the filter for better stability.
  • 💡 You might find that algae enjoy your baffle and begin growing on it over time. You can remove the baffle and rinse it with hot water to remove the unsightly guests. Algae-eaters may be able to scrub away the algae, but only if the baffle extends into the water. Depending on your tank setup, water level and the size of your baffle, it might stop short of the water.
  • 💡 If you're left with any sharp edges after making the necessary cuts, trim the problem areas so they're as smooth as possible.


  • Make sure you prime your filter if it is not self-priming. If you don't, the filter motor may become damaged.

Photo Credits

  • Jupiterimages/Comstock/Getty Images


Located in Pittsburgh, Chris Miksen has been writing instructional articles on a wide range of topics for online publications since 2007. He currently owns and operates a vending business. Miksen has written a variety of technical and business articles throughout his writing career. He studied journalism at the Community College of Allegheny County.