Is My Filter Too Strong For My Betta?

You got your tank set up, waited the necessary time to cycle the tank, and finally got your beautiful betta. The only problem – he or she seems buffeted about when trying to swim near the filter.

Or even worse, your fish can’t swim in the tank at all and spends all of his or her time hiding behind a decoration.
The problem is with your filter. Its current is too strong for your betta to handle.

Bettas Don’t Swim That Well

Bettas have a lot of pluses, but they are not strong swimmers. They take much more effort to get about than do most other fish, even common goldfish. They often need to wriggle their bodies from side to side to swim, instead of smoothly knifing through the water like other fish.

Male bettas of long or double-finned varieties have an even harder task swimming than short-finned males (called plakats) or females. Those gorgeous long, flowing fins come at a price. They considerably hamper a betta’s swimming ability.

If you have added a betta to your community tank and the other fish are fine with the current, your betta could still have problems. Since the other fish swim so much better, they will get all of the food, leaving your betta to starve.

Signs That the Filter Current is Too Strong for Your Betta

Watch your betta try to swim. If he or she seems knocked about by the water, then that’s a tell-tale sign the filter is too strong. If the filter only makes a current that affects part of the tank, the betta will spend all of his or her time in the part of the tank not affected by the current.

You also want to examine your betta and look for signs of illness that could cause erratic swimming behavior. These include:

  • Having a bloated abdomen
  • Swimming sideways or upside down
  • Torn fins
  • White spots
  • Your betta appears as if covered in cotton.

In this case, the betta needs treatment. If your betta looks healthy, then turn the filter off for one day. One day should not hurt your betta. If your betta starts swimming normally all over the tank, then it’s definitely the filter.

Make Sure the Filter is Small Enough for the Aquarium

One mistake that beginner fish keepers make is to get a filter that is made for much larger tanks than for what the tank size actually is. If you have a 10-gallon aquarium, please do not get a filter for a 30 gallon. This can create currents too strong for your betta.

Another problem with a filter that is too big is that it reduces the efficiency of the beneficial bacteria that live in the filter. These bacteria are essential to get rid of harmful toxins in the water like ammonia. 

The only option is to take out the old filter and get a new one. This time, get one that matches the size of your betta’s aquarium.

Softening the Current in Hang On the Back (HOB) Filters

Hang on the back filters, also called power filters or HOB filters can cause strong currents since filtered water falls to the tank like a little waterfall. There are several ways to soften the flow.

One easy and inexpensive way to make a baffle is from an empty plastic water bottle. Make sure the water bottle has NOT been cleaned or gone through the dishwasher. This can leave trace amounts of cleaner or detergent that can harm your betta. Once the bottle is empty:

  • Cut off the top and end of the water bottle with scissors.
  • Cut the remaining tube in half on one side only.
  • Place the cut side towards the place on the filter where the water flows out. The water bottle tube should hug this area, cutting back the force of the water.
  • Tape the water bottle in place.

You can also secure an aquarium-safe sponge to the water flow output area. If there is enough room in your cartridge holder, fit a little sponge in between the cartridge and the holder. This can help slow down the water flow.

Youtube: How To Reduce Flow With Hang On Back Filters by dmichaels fish den

Rearranging or Adding Decorations

You can also help break up the current by moving rocks, plastic plants and other decorations directly in the flow of the current. These objects help soften the current and create better swimming and living conditions for your betta.

Just be sure to choose decorations that do not have sharp edges, since they can easily tear your betta’s fins. Also, avoid painted decorations, unless you absolutely know for sure that the paint is safe for aquariums. If the paint starts peeling or chipping off, throw it out. 

Switch to A Sponge Filter

If the flow rate is still too strong for your betta, consider removing the hang on the back filter altogether and trying a sponge filter. They are efficient and not that bad to maintain, but you will need to hook them up with airline hose and place one end of the hose onto an air pump.

Sponge filters have a much lower flow rate than a hang on the back filter. They may not look as attractive as a hang on the back filter, but if it makes your betta happy, then the sponge filter is a beautiful thing.

When you clean a sponge filter, be sure to never run it under your tap. Chlorine and other chemicals in your water can kill off all of the beneficial bacteria in the filter. Instead, rinse it in old aquarium water.

To prevent making a big cloud of debris in the tank when you lift the sponge filter, place it in a plastic bag before lifting. You do not need to worry about the debris so much, since the rinsed filter will be able to suck it all up again in a few hours.

Special Note for Aquariums Under 3 Gallons Large

There are filters made for very small aquariums under three gallons. These are usually HOB filters or submergible filters, which are like HOBs but need to be completely in the water. There are sponge filters made for very small fish tanks. If these filters are too strong even after modification and rearranging tank decorations, just take the filter out. 

You’ll need to do more frequent partial water changes in order to keep your betta’s tank water healthy. You also should find a larger tank for your betta. Although bettas can live in very small tanks, they really blossom in tanks that are at least five gallons large.

You should still keep the small aquarium. It would make a great hospital tank. It is also good to have a tank for emergencies, should the larger tank break or have some other problem. 


You know the filter’s current is too strong when your betta constantly fights to swim without showing any signs of illness. There are many things you can do to soften the current. You may have to get a new filter. This will be money well spent to make sure you have a happy, healthy betta.

If you want more tips and guides on aquarium filters, please visit our collection of articles here.

About the author

Hi, I am Rena.
I grew up in a house surrounded by fish tanks.
I have spent my life caring for and writing about fish.
I have studied journalism and worked for online and print magazines.

You can find the articles I wrote here

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