How to Build a filter using a 55 gallon barrel
By Greg Bickal - (Greg's web page)
My Indoor Filter Setup
For my 800 gallon indoor pond, I use a quilt batting as a pre-filter, and a 55 gallon barrel filled with lava rock as a filter. To clean the filter, I turn off the pump, blow air through a pipe that runs to the bottom. This air backwashes the filter and shakes loose the detrus. I then drain about 30 gallons of dirty water from the filter. Then turn the filter back on. This filter sustains 22 large Koi.
Barrel filters are an inexpensive way to provide filtration for a small to medium sized pond. Designed for a flow rate of around 1200 gph, they can hold around 3 cubic feet of media.

Materials
ItemQty DescriptionSize Cost
A1Barrel 55 gallon

$5
B1Bulkhead Fitting 1"

$5
C1

Bulkhead Fitting

2"

$10
D1PVC Pipe 4" Sewar, Schedule 20

$2
E5Bricks 4" x 8" with holes

$2
F1Wire 12 gauge, 10' long

$1
G3Lava Rock 50lb bag, large

$15
     

$35


Assembly (about 2 hours)
  1. Cut the top out of the barrel. Do this very carefully cutting as close to the edge as you can.
  2. Cut a hole in the center of the lid, the same diameter as the sewar pipe.
  3. Drill 1/4" holes in the lid, (as many as possible).
  4. Put a 1" bulkhead fitting on the bottom of the barrel. This will be used as a bottom drain and the air-backwash system.
  5. Put a 2" bulkhead fitting at the upper rim of the barrel (back to pond). You may have to use a torch to warm up the side of the barrel so you can mold it flat for the fitting to go on correctly.
  6. Space about 5 bricks on the bottom of the barrel and then put the barrel lid over the bricks. This gives the gunk somewhere to settle and also lets the water comming in spread out over the filter.
  7. Cut the pipe to be used for the downward feed. Place it through the hole in the barrel lid at the bottom. Wire the top of the pipe to the top of the filter in 3 places so that it stays in the exact center.
  8. Pour lava rock into the filter.