Fluidized bed filters pros and cons?

[Kribensis]

What are the pros and cons of a "Fluidized bed filter"? And would it work well for a cichlid aquarium (fresh water tank)?

 

[BillD]

The big advantage is the large amount of surface area of the bio media (sand) relative to the volume. Their function is strictly biological. The media is cheap (silica sand) and the filter doesn't need to be large. there isn't any maintenance because debris isn't trapped if set up correctly. Prefilters can keep debris from actually entering the filter.
They can be tricky to balance the flow so you don't have the sand getting into the tank but still have it in constant motion. That is more of a design issue, wherein you have to have much more flow coming into the filter and greatly reduced when it leaves so the sand is turned over but isn't carried out the return. A cone works well for this.
There was a nearby African chiclid breeding operation that used one to filter their entire 40+ tank setup, and if I remember correctly, it was a 3" or 4" PVC pipe 4' high. I don't recall the depth of the sand.