Personally, I have had bad experience with the Rainbow Lifeguard Fluid Bed filters, and could never recommend them to anyone. I have a retail store with approximately 7,500 gallons of water hooked into a handful of central filter systems. Our initial design was to use FB900's on a manifold to provide biological filtration. We had 12 of them all together.
The problem is this: when there is a power failure, water draining out of the unit carries sand with it, which jams in the hose. Fine sand packs very tightly, and even very large pumps cannot dislodge it once it has settled. The units feature a check valve which is supposed to prevent that, but we found in nearly every case the check valve was defective. In communications with Rainbow Lifeguard they admitted that this is in fact not an uncommon problem. Eventually we gave up and scrapped the units, choosing to replace them with large fiberglass units that I custom built for the purpose. Fluid bed filters really are simple to make, so if you are at all inclined to that kind of thing, I'd say give it a shot.
BTW, the company that bought Rainbow Lifeguard is Pentair Aquatics, a division of PAC-FAB, one of the largest swimming pool pump and equipment manufacturers in the world.
Hope this helps.
-- Alastair
