The idea behind a fluidized bed filter (just in case anyone hasn't seen one before) is that sand has quite a bit of surface area. However, just dripping water through it doesn't give the bacteria very good access to the media, and it drips in inefficient patterns. To solve this, water is pumped up through the sand evenly to "fluidize it", causing it to flow evenly in the water and give the bacteria constant access to the entire surface area of each grain. This produces an exorbitant amount of bio-filtration and, because of the constant bumping of the sand, it is entirely self-cleaning. Miles recommended getting one, and here it is!

This is the media. I know I could have used sand-blasting sand or something cheaper, but my DIY brain needs a bit of a rest due to heavy work schedule and house-cleanliness demands.

Here is the filter, running beautifully! (Yes, it is running at
exactly the maximum operating line.

)

These are just some more pictures of it running off of the sump. I ghetto-rigged a hose-clamp to function as the check valve, because the stock one is teh suxorz and I am currently using a powerhead that is
way too strong for the little 600 gallon model.
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Here is the picture of the 900 gallon model that we've also got. I eventually want to run it on the pair of 523 gallon tanks, but I'm probably going to set it up to cycle on the 150 hospital tank.
Thank you Ashley, for taking the pictures. I hope it helps your birthday present handle rays better!
