Here's another Do-it-Yourself project that's quite easy and will give you good service when assembled properly. Unfortunately I didn't detail this project with many photos so I'll do my best to explain it in detail. Here's the picture of the finished FBF (Fluidized Bed Filter), and I'll try my best to walk you through it.
The materials required are:
4" thin-wall pvc sewer pipe, not the standard thick-wall schedule 40.
3-4" thin-wall pipe caps
1-4" Y-fitting-this needs to be made of styrene, it's fairly translucent, and you'll need it so you can view the sand level during filter operation
1-4" street 45 fitting, this has a small end and a large end, this keeps the FBF tower shorter in height, a standard 45 will work but you'll end up w/ a taller uneven tower.
2-3/4" bulkhead fittings
1-Holesaw to cut openings for bulkheads (get the bulkeheads first, to assure you get the proper holesaw for the bulkheads' diameter)
These filters are very efficient biological filters, the above filter contains enough sand for a 900gallon tanks' worth of bio-load. Although they work well in any tank over 75 gallons. It's preffered to use a sump w/ the FBF, this will provide an area for mechanical & chemical filteration, and a place to put the submersible pump.
Measure the height you'll have available and make the filter tower as high as you can. The above filter measures about 30"high, this allows room for the sand to "fluidize" w/out flowing into the tank.
Start construction by cutting out the sections of the 4" sewer pipe to make the FBF the desired height, hand-fit the pvc pieces to assure the right lengths are attained.
Once you get the FBF tower the desired height, cut holes in the top two pvc caps w/ your holesaw, try to center the holes as best as you can. Once the holes are cut, insert the bulkheads into the caps, keep the rubber washers to the inside of the caps, and tighten the fittings. Once this is complete, you need to measure a section of 3/4"pvc to go down the inside of the sewer pipe. The straight section of the Y contains the 3/4"pipe (the incoming water), the arm of the Y is the output to the tank. The section of 3/4" pvc MUST have a 3/8-1/2" gap from the bottom cap, this will allow the water to disperse the sand inside the filter, if the gap is too small it will restrict pump flow, if it's too big the sand won't disperse evenly and water will tunnel through the sand rather than spreading the sand out inside the FBF. After getting the downpipe cut, perform a test fitting, making sure all lengths are acceptible.
Once you're satisfied w/ the cuts, go ahead and prime&cement all fittings EXCEPT the top output cap, this will be sealed after adding sand. Be liberal w/ the cement, better too much than too little!
Fill with sand, it's a good idea to wash the sand prior to this, it can be quite dusty. Fill to the point where the bottom sewer pipe meets the Y (on the above pic, it's the point where you see the handwritten #'s end, right below the lower lip of the Y fitting).
Go ahead and seal the last top cap, fill w/ water and check for leaks, you won't have any if you were generous w/ the cement).
Place pump in sump, make sure flow valve (this comes w/ the Rio pump) is accesible, then add check valve to output of flow control, (make sure valve is in the right flow direction) Put barb fitting on output of check valve, and run vinyl tubing to input of FBF, you may want to use a barbed "L" fitting here. Use vinyl tubing for the output of FBF to tank as well. Once you get all the hoses cut to length, take filter along w/ the check valves out, and pressurize filter w/ a garden hose, just turn on the hose full blast and you'll eventually get enough pressure to "blast through" the clogged sand. This will keep the sand in a "fluidized" state as long as you don't remove the check valve. If you don't do this step the Rio pump won't have enough force to unclog the sand and the filter won't flow. Replace filter and re-connect to pump, the pump should flow freely. You'll want to adjust the sand level once the filter is flowing, just enough to see rippling on top of the sand, not too much or the sand will blow into the tank. Just use a flashlight and shine it to the back of the Y, you'll see the sand level, use the flow control to adjust to the optimum level. Sorry for the lack of pictures, hopefully you get the idea. BTW, you can make a smaller version of this filter using 3" thinwall pipe & fittings, and 1/2 downpipe and bulkheads for tanks in the 55-100gallon range and a Rio 1400 pump. Here's a pic of the tanks' inner workings. It shows the pumps & checkvalves a bit clearer. BTW, I use pairs in all my filters so I can service one and still keep bacteria action in the tank, or in case of a pump problem, I'll still have a working unit, just something to consider in your filter plans.