Fluval U Series Underwater Filter

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; and U4 includes: 2 foam filter pads, 2 poly-carbon cartridges and 90 g BioMAX.

Downloadable Fluval U Series Underwater Filter Instruction Manual PDF
(Requires Adobe Acrobat Reader 4.0 or later - get it here for free)

Please click on "More Information" for filter maintenance tips.

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.