Fluval U4 and Fluval U Series Submersible Aquarium Filter Review

OB Guy

Administrator
Staff member
Fluval U1, Fluval U2, Fluval U3 and Fluval U4 Series Underwater Fully Submergible Aquarium Filter Review:

The Fluval U4 filter and Fluval U series aquarium filters are one of the best if not the best fully submersible underwater aquarium filters on the market in my opinion. I have three Fluval U4 filters that I have used in many different aquariums form turtles tanks to Cichlid tanks. The Fluval U4 is very easy to clean and maintain and works great on it's own or as a secondary filter for your aquarium. The output on the Fluval U4 is very powerful and is also good for moving water on the surface. It's like having a powerhead with the added benefit of additional filtration. I have never used the Fluval U1,U2 or U3 but the design is the same on all the Fluval U series filters just different in size. I would highly recommend the Fluval U4 for anyone needing a submersible filter for their aquarium.

Overview:
*Fully submersible aquarium filter for enhanced filtration options
*Boost aquarium filtration, water movement and crucial aeration
*Underwater filter features flip-top access for easy media change

Open your eyes to a world of unsurpassed underwater aquarium filtration. The versatile Fluval U Series Underwater Filter offers creative new possibilities for aquarium filtration, water movement and crucial aeration in freshwater and saltwater aquariums. Fully submersible filter suction mounts virtually anywhere inside your aquarium, making it the perfect solution for setups where external filtration is not possible. Place horizontally or vertically in your aquarium or even in sump-style filters for added filtration. Adjustable flow rate and directional output nozzle lets you direct water movement where you need it most. Venturi system introduces vital oxygen for a healthy aquarium environment. The top-loading Fluval U Series filter features flip-top media chamber access for fast, efficient maintenance. Quiet running units are easy to install and maintain as primary aquarium filtration or as the ideal supplemental filtration in larger systems with heavy fish loads. Also great for terrariums and turtle tanks.
U2, U3 and U4 feature adjustable 3-way flow to give you custom water movement in your aquarium. Choose top output for maximum circulation and oxygenation, spray bar output for gentle flow in planted aquariums, or bottom output for deepwater agitation.

  • U1 includes: 1 foam filter pad
  • U2 includes: 2 foam filter pads, 2 poly/carbon cartridges, and 40 g BioMAX
  • U3 includes: 2 foam filter pads, 2 poly-carbon cartridges and 40 g BioMAX
  • U4 includes: 2 foam filter pads, 2 poly-carbon cartridges and 90 g BioMAX.
Model
Stage 1 Filter Foam
Bio/Mechanical Filtration
Stage 2 Poly/Carbon Cartridge
Chemical Filtration
Stage 3 BioMax
Biological Filtration
U2
X​
X​
X​
U3
X​
X​
X​
U4
X​
X​
X​

Specifications
ModelAquarium SizeFlow RateDimensionsWattage
U115 gallons65 gph2-1/4" x 2-3/4" x 5-3/4" high5W
U212-30 gallons105 gph3" x 3-1/2" x 8" high5W
U324-40 gallons155 gph3" x 3-1/2" x 10-1/2" high7.5W
U434-65 gallon260 gph3" x 3-1/2" x 13" high12W

Maintaining the U1 Filter
Warning:
Always disconnect appliances in the aquarium from the electrical supply before placing hands in the water, before putting on or taking off parts, and whenever the filter equipment is being installed, maintained or handled.
Following a routine maintenance schedule will result in a healthier aquarium and extend the life of the filter. Fluval filters have been designed to facilitate these tasks as they can be done within a matter of minutes. For best results please follow our maintenance schedule recommendations.
Filter Cartridge Replacement
Replace Foam Pads every 3-6 months. (This is the only media this filter requires.)
U1 Filter Maintenance
Clean Impeller and Impeller Well every 4 months. Replace impeller yearly for optimal performance and to prevent wearing. Clean filter body once a year.
How to Replace the Filter Cartridges
Important:
To enhance bacterial action, pour a dose of biological aquarium supplement onto your filter cartridge each time you change the media.
  1. Unplug the power cord.
  2. Open the filter cover.
  3. Slide the foam out of the filter body and place it in an empty bucket. Rinse the foam cartridge using water taken from the aquarium or replace the foam following the recommended replacement schedule. Do not use tap water as this will kill the beneficial bacteria in your foam. Note: Never use soap or detergents as these products could be harmful to the inhabitants of your aquarium.
Maintaining the U2, U3 and U4 Filters
Warning:
Always disconnect appliances in the aquarium from the electrical supply before placing hands in the water, before putting on or taking off parts, and whenever the filter equipment is being installed, maintained or handled.
Following a routine maintenance schedule will result in a healthier aquarium and extend the life of the filter. Fluval filters have been designed to facilitate these tasks as they can be done within a matter of minutes. For best results please follow our maintenance schedule recommendations.
Filter Cartridge Replacement
Replace 1 Poly/Carbon cartridge every 2 weeks. Replace Alternate Foam Pads every 3-6 months. Replace half quantity of BioMAX nodes every 5-6 months.
Filter Maintenance
Clean Impeller and Impeller Well every 4 months. Replace impeller yearly for optimal performance and to prevent wearing. Clean filter body once a year.
How to Replace the Filter Cartridges
Important:
Do not replace all filtration cartridges at the same time. Alternate filter cartridge changes so that some older cartridges remain in use. This ensures the re-seeding of beneficial bacteria, so that colonies discarded with older cartridges will be replaced by vigorous new ones. To enhance bacterial action, pour a dose of biological aquarium supplement onto your filter cartridges each time you change the media.
  1. Unplug the power cord.
  2. Open the filter cover (To make the operation easier and in case the filter is positioned under an aquarium frame, tilt the filter forward until it stops but make sure there is enough electrical cord to allow the filter to pull forward).
  3. Slide the foam cartridge frames out of the filter body. Keeping them vertical to avoid releasing the debris collected inside the debris receptacle. Place them in an empty bucket.
  4. Remove the poly/carbon cartridge from the cartridge frame.
  5. Remove the foam. Rinse the debris receptacle and the foam pads using water taken from the aquarium or replace one of the foams following the recommended replacement schedule. Do not use tap water as this will kill the beneficial bacteria in your foam. Note: Never use soap or detergents as these products could be harmful to the inhabitants of your aquarium.
  6. Replace the foam pad. Make sure the foam is positioned behind the tabs on the sides of the frame.
  7. With the carbon side facing out, re-insert the poly/carbon cartridge by inserting the lower end of the cartridge into the lower end of the cartridge frame then snapping the top side of the cartridge under the two tabs on the top side of the frame. Do not press too hard, as the cartridge must sit on the top of the tabs on the sides of the frame. Hint: For best results replace 1 poly/carbon cartridge every 2 weeks.
  8. Slide the BioMAX cartridge out and place it in the sink or bucket.
  9. Pull open the tab on the side of the cartridge, opening the cover. Rinse the BioMAX with aquarium water, never tap water, or replace half the quantity every 5-6 months. Never replace all the BioMAX nodes at one time, as valuable colonies of beneficial bacteria would be lost.
  10. After rinsing, put the BioMAX back in cartridge and close the cover. For best results completely fill the cartridge with BioMAX nodes but allow the cover to close easily.
  11. Re-insert foam cartridge frames into the filter with the poly/carbon pad facing inwards. Re-insert the BIOMAX cartridge into the filter making sure to properly align the hole at the bottom of the cartridge directly on the top of the impeller opening. Close the filter cover and if required snap the filter body back into position on the filter bracket.
 
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