How a fluidised bed filter system works
A fluidised bed unit takes the biological filtration out of the tank and supersedes outdated substrate systems.
Silica sand is held in suspension in tank water pumped through an external cylindrical container. This has the added benefit of allowing the sand molecules to move around as opposed to being packed together. This allows for a larger surface area to be created for beneficial bacteria colonisation. This produces a much more efficient conversion of ammonia into nitrite then into nitrate.
Certain systems include a carbon filter cartridge which removes any colouration from the water before being pumped back into the aquarium. The fluidised system is quite consuming in regards to oxygen and water being pumped back into the aquarium should be given every chance to re oxygenate. A spraybar is a good method plus using an airstone or a venture system fitted to the outlet to re oxygenate the tank.
The problem with this system is when a power failure happens. If the power goes out all of the suspended sand in the system will fall and compact and you may need to give the system a little help re suspending the sand. The system may need to be put on full power to get it started again. If the filter is shut off for a long period of time the bacteria colony may die off and will need to be re established.
A typical fluidised bed filter. The sand is held in suspension creating a moving biological bed. A valve in the unit prevents sand from siphoning back into the pump if the power fails.