DIY Project - Biological Filter
DIY - Biological Filter
Custom built biological filters can save you a ton of cash but have inherent risks associated
with them. What I mean by risks is that there are the very real possibilities that the bucket
may crack, a seal may fail, or the whole thing might just backup and drain your entire tank
onto your floor. I am not attempting to scare you but simply stating all the things I have
experienced over the years.

Rule number one of building an external filter is expect the worst. This is a design that
works for me, perhaps it won't for you. Look it over, compare it to other designs, and adapt
it to meet your needs. I will state that I have maintained excellent levels of pH, nitrates,
nitrites, and ammonia using this filter on tanks ranging from 30 - 150 gallons.

The addition of an overflow pipe and extra holes throughout the inner drain pipe will
prevent the accidental clogging and draining of your entire tank onto the floor. It may seem
like overkill but I have 126 reasons...the 125 gallons that ended up on my floor and my wife.

You will need a 5 gallon bucket
with a lid - found at any local
hardware store.
Do a dry fitting of all parts
prior to a final assembly to
make sure everything fits.
Spray bar parts:
1/2" T-fitting (1)
1/2" elbow (2) - prevents back
ups should the spray holes get
3" x 1/2" PVC for arms
5" x 1/2" PVC for neck

Spray holes are 1/8"
Inner Drain Parts:
10" x 1" PVC with 3/8" holes
1" Threaded/Slip Adapter (2 -
one male and one female)
Overflow Pipe:
14" x 1" PVC Pipe
1" Slip Elbow with threaded end
1" Threaded/Slip Adapter
1" Slip Elbow
Inner Drain:
Drill a 1 1/4" hole about two inches
from the edge of the bucket. The
rubber seal (inside & out) is scrap
45 mil EPMD liner. Silicone is used
on both sides of the EPMD seal.
Inner Drain:
Silicone the EPMD seal (both sides) and thread 1" male adapter up
through the bottom into the female and tighten. Allow silicone to
cure for 24 hrs. Slip 1" PVC coupler onto male adapter.
Inner Drain:
Slide 10" PVC drain into female
adapter. Keep bucket up on
books to keep from bumping
bottom drain.
Inner Drain:
Cut rigid 3/4" plastic screen to
fit. Keep 4" from the bottom
using scrap PVC supports.
Filter Material:
Cut the foam material to fit and
slide down over drain.
Filter Material:
Next add the screen material.
Filter Material:
Cover the entire area with
bio-balls, lava rock, scrubber
pads or any other material for
the bacteria to colonize.
Filter Material:
Add refillable filter cartridges
with activated carbon.
Set the filter up on a raised
surface and drill another 1 1/4"
hole near the top of the bucket.
Filter Material:
Fill remaining space with
polyester filter floss.
Filter Material:
Cover floss with plastic mesh
screen to capture large
Spray Bar:
Insert spray bar, make sure
water does not go directly into
Cut a 1/2" hole in the lid to run
the tubing from the pump.
Place a ring of silicone on the
both the inside and outer
surface of the bucket. Thread
the 1" slip elbow through the
hole and tighten the adapter.
Smooth the silicone around the
Twist the overflow pipe into the
elbow. I ended up removing the
second elbow.
Bottom Drain:
The bottom drain pipe is a 6" x
1" PVC pipe with a 1" slip elbow
to direct the water outward
across the surface of the tank.
Shopping List:
5 gallon bucket [~$5.00]
48" x 1" PVC [~$3.00]
48" x 1/2" PVC [~$3.00]
(2) 1/2" slip elbows [~$0.50 ea.]
(1) 1/2" slip T-joint [~$0.50]
(2) 1" slip/threaded female adapter [~$0.90 ea.]
(1) 1" slip/threaded elbow [~$0.90]
(1) 1" threaded male adapter [~$0.90]
(1) 1" slip coupler [~$0.90]
(1) 1" slip elbow [~$0.90]
1 tube of 100% Silicone [~$4.00]
1 bag of polyester filter floss [~$3.00 for a small bag in a craft department]
[for $16.00 you can buy a 10lb box in most craft departments - a.k.a.pillow stuffing]
1 electrostatic washable furnace filter [~$20.00] this will supply you with the rigid plastic screen,
foam, and screen materials.
1 bag lava rocks for a gas grill [~$5.00]
(2) large refillable whisper filter cartridges [~$8.00 for a box of 4 - includes activated carbon]

Total price: approximately $58.00 USD - with enough material left over to be well on your way to
build a second filter. The pump and tubing will be extra depending on your needs. Be careful not to
over work the filter as the water should be draining at the same rate it coming in or you run the
risk of overflowing the filter and flooding the room. - all rights reserved 2007-2010