First you need to figure out how big of a filter you will need. We took the following tips from Moorehaven Water Gardens.
      Size your pump so the entire pond volume will pass through the bio filter once every two to three hours.
      The ideal rate of filtration is 1/2 gallon of water per minute per square foot of filter bed. If your filtration is too fast it will result in insufficient exposure time to the bacteria. That's right, it's the bacteria that makes the bio filter work.
      To calculate the size of your filter, figure the pond volume in gallons (width x length x depth x H1) and divided by 60 (minutes). This equals the square footage of your filter bed. The bigger the better, if you have room. Remember that this is the TOTAL area of filter material when you put it in your system it will be cut up or rolled up.
      To size your tank figure the filter for 1/2 of the tank, in the middle. Then 1/4 of the tank will be for silt on the bottom and 1/4 of it will be for the top.

      The second step is getting together all the material and planning the project. Since projects vary by size I'll tell you what I got and you can go from there.

• 3/4" PVC Pipe (2)
• 2" PVC Pipe (1)
• 1" PVC Pipe (1)
• 2" 90 Degree Elbows (2)
• 2" Male Adapter, for 1/2 of bulkhead adapter
• 2" Female Adapter, for 1/2 of bulkhead adapter
• 1" Male Adapter, (2), for 1/2 of bulkhead adapters
• 1" Female Adapter, (2), for 1/2 of bulkhead adapters
• 1" 90 Degree Elbows (1)
• 1" PVC Pipe to Garden Hose Fitting (2)
• 3/4" 90 Degree Elbows (8), for supports
• 3/4" Kris Cross Fitting (2), for supports
• 44 Gallon Rubbermaid Trash Can
• Egg Crate Louver from overhead fluorescent light fixture, for supports
• Washable/Reusable Furnace Filters (10)
• Water Pump sized per the above instructions
• Small Rubbermaid Roughtote to house the pump
• 3/4" PVC fittings to get from the pump to a garden hose on the outside of the box.