I haven't used one, but the concept behind them is pretty obvious. I would expect them to work well, but if the media ever stopped moving, I'd expect them to continue working just as well :lol:
I've built a
Fluidized Bed Filter (FBF) for my 240G when I first set it up, but am no longer using it. From what I see, a 'moving bed filter' is the poor man's FBF. The smaller the particles, the larger the total surface area is going to be. Sand is hard to beat in this regard, and the moving bed filter has much larger particles.
By moving the particles around you optimize the percentage of the surface that can actually be used effectively, because no part will be permanently covered by something else. That would usually be a huge problem with sand, but is no great problem with media that are less densely packed, such as bio balls or things in moving bed filters. That's why moving large particles around will have a much smaller effect than for example with sand.
The reason I am personally no longer using FBFs - or any specialized bio filter media - is that I don't believe available surface area is usually the limiting factor for bio filtration. Especially when things go wrong, oxygen content in the water can become a limiting factor. That's why I try to keep oxygen at saturation levels. If that's the case, nitrifying bacteria will always find surface area to colonize - be it in the tank or in the filtration system.
In short, I think a moving bed filter will be overkill for bio filtration, because the media will provide more than enough surface area even in the non-moving state. But to each his own. Having your bio filtration media move around certainly can't do any harm :thumb:
