Fluval Aquarium Underwater Filter

By Fluval
Rated 3.5349 out of 5 stars


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$38.99Chewy Price
$79.99Chewy Price
In Stock
FREE 1-3 day delivery

About This Item


  • Optimal water filtration system for aquariums that ensures proper oxygenation for clear water and a healthy environment.
  • Fine foam pad traps small debris while bio-foam captures larger debris and nitrifying bacteria.
  • Adjustable 3-way flow control—top output for circulation and oxygenation, integrated spray bar for a gentle even flow, and bottom output for deepwater agitation.
  • Convenient flip-top lid allows for quick and easy access to filter cartridge for maintenance or replacement.
  • Ideal for freshwater, saltwater and reptile environments.

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Play Video: Learn More About Fluval From Our Team of Experts
Learn More About Fluval From Our Team of Experts

Compatible Products

Ensure your system runs smoothly with Fluval accessories.

Frequently Bought Together

This Item – Fluval Aquarium Underwater Filter, 24-40 gal
Rated 3.5349 out of 5 stars
$38.99Chewy Price
Fluval U2 Poly/Clearmax Filter Cartridge, 2 count
Rated 3 out of 5 stars
$9.49Chewy Price
Fluval U2 Foam Pad Filter Media
Rated 3.25 out of 5 stars
$2.92Chewy Price
Total Price: $51.40

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Fish TypeMarine Fish, Tropical FreshwaterMarine Fish, Tropical FreshwaterBetta, Cichlid, Goldfish, Tropical FreshwaterBetta, Bottom Feeder, Cichlid...Tropical Freshwater
Aquarium TypeSaltwater, FreshwaterSaltwater, FreshwaterSaltwater, FreshwaterSaltwater, FreshwaterFreshwater

Questions & Answers

20 Customer Questions

I just installed my U3 in a turtle tank. People were bragging about it being very quiet. Mine is not. Is this filter supposed to be soundless? I'm new to this and I don't know anything about filters. Somebody gifted my 4 year old with a baby turtle and I'm trying to do my best to take care of it.
Answer by ChewyNov 27, 2017
Typically the filter will make noise if the water level is below the filter. We encourage pet parents to fill the tank 2 to 3 inches above the filter to prevent this.

Can I use this for my Betta fish, how fast is the flow?
Answer by ChewyJan 10, 2018
This Filter allows for adjustable flow and will be suitable for a tank with a Betta.

What size is best recommended for a 75 gallon tank? Thank you!
Answer by ChewyFeb 04, 2018
The U1 is suitable for up to 15 gallon tanks, the U2 is for 12-30 gallon tanks, the U3 is for 24-40 gallon tanks and the U4 is perfect for 34-65 gallon aquariums. At this time this model does not have an option for a 75 gallon tank.

What is the “Venturi aeration system? How is it used?
Answer by ChewyApr 19, 2018
A venturi creates a constriction within a pipe (classically an hourglass shape) that varies the flow characteristics of the water travelling through the tube. As the fluid velocity in the throat is increased there is a consequential drop in pressure. . If the Venturi System is to be used, place the Venturi valve into the top of the vent. In order to have the airflow/venturi work properly, it must remain above water.

ReviewsWrite a Review

Rated 3.5349 out of 5 stars
86 Ratings
Would recommend to a friend

85 Customer Reviews

Rated 1 out of 5 stars
By Beth on Nov 28, 2023

not cleaning the water

bought this for a turtle tank. I have a 55 gallon tank that is about 1/3 full with my 2 full grown red-eared slider turtles. filter appears to work in that it runs, media gets dirty, water does come out. I have even removed and replaced at least half the water in the tank. However my tank water continues to get worse and worst.

Rated 2 out of 5 stars
By Yuck on May 15, 2023

Not worth it

Bought this for my turtles tank. Very disappointed. After the first few weeks it stopped filtering properly. We had to clean the tank every week just to keep up with the demand that the filter wasn't. Now it's been just over 2 months and it stopped working all together. Save your money anf find better a different filter.

Rated 5 out of 5 stars
By annemal on Dec 1, 2022

Very quiet

I bought the Fluval U4 when I made the recent transition of my goldfish from a 39 to a 55 gallon tank. Since this tank would be located near the bedroom, *quiet* was one of the top criteria of the new filter. The Fluval filter has indeed delivered on its promise to be quiet. It is marginally audible at all, fully submerged in the water. This is in stark contrast to the previous filter I used, a hang-on-back style filter that created so much ambient noise it was a constant distraction. There is an optional valve that can be installed on top of the U4 that pulls in air to push bubbles out with the water. However, this requires the top to be above the water line, and I found this to be a bit too noisy for my liking. Instead, I have an air stone bubbler set up in front of one of the jets of this filter, such that it pushes forward a column of bubbles that the fish love. It's easy to disassemble and clean, and relatively unobtrusive in a 55 gallon tank. So far, I'm very happy with my purchase

Rated 5 out of 5 stars
By Sage on Apr 15, 2023

Fabulous filter

This filter is awesome. No more listening to water run. It keeps water clear and is absolutely silent.

Rated 1 out of 5 stars
By Rc69 on Mar 17, 2023

No suction cups

I ordered alot of thing for my sons new turtle. I would love to use the filter but it did not cone with suction cups

Rated 1 out of 5 stars
By Dirty on Feb 22, 2023

Not Keeping Tank Water Clean

This thing just simply does not do a very good job at all. Water has never been so dirty.

Rated 1 out of 5 stars
By tank on Aug 17, 2022

Doesn’t clean well

i’ve had this turtle tank for less than 3 months and it doesn’t keep my tank clean the water is murky within 3 days after cleaning it out.

Rated 3 out of 5 stars
By Manda on May 28, 2022

Mixed Feelings

I have really mixed feelings on this. I’ve had it for 4 months and it’s worked amazing! Super easily to clean, adjust water flow, and I love the sleek look. Today I unplugged it to clean it then plugged it back in and it won’t run. Regardless of what I do. Like the other reviews said, really frustrating. I haven’t decided if I’ll buy another because I really like the filter.

Rated 3 out of 5 stars
By None on Aug 22, 2022

Some success.

Haven had this long but of the three internal filters I bought, this one is the quietest and easy to use.

Rated 3 out of 5 stars
By Lobo on Apr 21, 2022


My cats love the chunky Turkey, so I figured we’d give this a try. They won’t touch it. Too bad. They are so picky. I’ve tried so many FF flavors, and even the flavors they used to eat they will not touch.