Fluval U2 - Filter Cartridge Replacement

[vcmtik]

I have just purchased a new Fluval U2 filter for my aquarium, under the recommendation by the shopkeeper that it is low maintenance and cheap to run. I notice that I need to change the black cartridge every two weeks. I have been looking at prices for replacements and they seem to be expensive. Can anyone tell me:

Is it necessary to change fortnightly - or could I rinse them in aquarium water.
If it is necessary to change - where is the cheapest place to buy replacements.

 

[Truck]

I have just purchased a new Fluval U2 filter for my aquarium, under the recommendation by the shopkeeper that it is low maintenance and cheap to run. I notice that I need to change the black cartridge every two weeks. I have been looking at prices for replacements and they seem to be expensive. Can anyone tell me:

Is it necessary to change fortnightly - or could I rinse them in aquarium water.
If it is necessary to change - where is the cheapest place to buy replacements.

you dont even need the carbon...just fill it with ceramic media instead

 

[vcmtik]

I have just purchased a new Fluval U2 filter for my aquarium, under the recommendation by the shopkeeper that it is low maintenance and cheap to run. I notice that I need to change the black cartridge every two weeks. I have been looking at prices for replacements and they seem to be expensive. Can anyone tell me:

Is it necessary to change fortnightly - or could I rinse them in aquarium water.
If it is necessary to change - where is the cheapest place to buy replacements.

you dont even need the carbon...just fill it with ceramic media instead

Thanks for the reply - I shall do that instead