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DIY Wet/Dry Filter
A Wet/Dry Filter (also known as a Trickle Filter) is a very efficient filter,
providing mechanical, biological, and optionally chemical filtration. Water
flows from the tank down to the wet/dry filter. Upon entering the wet/dry,
the water flows thru a filter pad, providing mechanical filtration to remove
particles of waste. Then the water passes thru a drip tray which spreads
the water across the surface of the biological filtration. The biological
filtration is usually some kind of bio-filter media, such as bio-balls. This media
simply provides room for bio-filter bacteria to grow. The dripping action of
the wet/dry provides a very high-oxygen environment for the bacteria. The water
flows past the biological media, into the main sump. From there, the water
is then pumped back up into the tank.
Here is a simplified diagram showing the whole system:
This page shows the details of the Wet/Dry itself. The details on the
overflow box are shown HERE.
If you want to see some quick-and-dirty pics of the actual setup,
here's a page I whipped up for it. But I'm warning
you, it isn't pretty!
If you know anyone who's handy, and has small workshop, it's easy to
make your own wet/dry. A table saw is probably the most important
tool, as it's very important to have smooth straight cuts where you
want to join the acrylic pieces.
I was given an old 29 gallon tank that I converted into a wet/dry.
Even if you were buying the tank, it wouldn't be too much for a 10-20g
tank.
Total cost was
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$10.00 for acrylic sheets, and a piece of plastic "egg crate" (from a
local plastic dealer, from the scrap bin)
$5.00 for acrylic adhesive (it melts the acrylic together)
$5.00 for silicon adhesive (to join acrylic to glass)
$15.00 for bio-balls (I got 3 gallons worth on sale)
$5.00 for pre-filter sponge (used a aquaclear 500 sponge)
$5.00 for filter pad to put in drip-tray.
$30.00 for return pump (I got a rio 2100, working fine)
$20.00 for misc. plumbing parts to get water from the overflow down to
the wet/dry, and to get water back to the tank from the wet/dry.
I used a overflow that I already had onhand, but it's not too hard to
make it yourself. Or you can buy a nice one for $50.00.
I'm very happy with my wet/dry. And the large sump tank is perfect,
since it lets me put my heaters, thermometer probe, and CO2 reactor
in the sump, instead of cluttering up my tank. I also like the way
the overflow box keeps the water surface perfectly clean.
I clean the pre-filter sponge twice a week (1 minute each time), and
the filter pad on the drip-tray once a week (5 minutes).
After having the wet/dry, I wouldn't use anything else.
Drawings of the wet/dry construction
These drawings only show the main wet/dry unit, not the overflow box, or
the plumbing. I'll add more detail to this later.
Details on the overflow box can be found here
Basic operation / concept
- Water flows from the overflow/syphon box on the tank, down a hose, to the
drip tray.
- The drip tray has small holes drilled in it, every inch or so. The tray
has a raised 1" tall lip all the way around it. This allows water to pool in
it, and drip thru the holes down into the bio-ball compartment.
- A large piece of filter pad is cut to fit into the drip tray, to provide
mechanical filtration, and to prevent junk getting to the bio-ball compartment.
- The bio-balls, supported by a piece of plastic "egg crate", provide room for
the biological filtration bacteria to grow. The number of bioballs varies.
For my 75g tank, I'm using 3 gallons of bio-balls.
- The water flows thru the bio-balls, and into the sump space. The sump space
(the area between the bio-ball compartment and the pump compartment) is useful for
placing things like heaters (I've got a pair of Ebo-jagers laying down along
the bottom, in the middle area, and running under the bio-ball compartment.) I also
have a temperature probe and a CO2 diffuser in the sump, so I don't need to clutter
the tank with all this stuff.
- The water then flows past a partition, into the pump compartment. I place
a sponge into the hole between the sump space and the pump compartment, to provide
one last chance to catch anything before it gets to the pump.
- A submersible pump placed in the pump compartment pumps the water back up to the tank.
Basic Construction
Everything in the picture, except the main tank, is made from 1/4" acrylic.
1/4" seems a little excessive, but it helps to prevent warping/bending. And
1/4" isn't really any more expensive than the thinner stuff. Look in your
local yellow-pages for a plastic dealer. I found one in my area that has a
scrap bin. I got all the acrylic I needed for my wet/dry for under $10.00.
Anywhere that acrylic is bonded to acrylic, I used a special acrylic adhesive
sold by the plastic dealer. It actually melts the two pieces of acrylic
together.
Anywhere that acrylic is bonded to the glass tank, Silicone sealant is used.
Be sure to get some that is aquarium safe. I found a tube at my local
hardware store for $5.00. The same stuff at the fish store is $10.00.
The acrylic partition at the left side just seperates the pump from
the rest of the sump. It helps to keep any sediment away from the pump.
Just measure the piece, cut the opening, and silicone the piece in place.
Make sure it's wide enough for your submersible pump to fit in the pump
compartment.
The next partition forms one wall of the bio-ball compartment. It should sit
an couple inches above the bottom. It has a small shelf along the bottom, to
support the "egg crate", and a small shelf near the top, to support the drip
tray. Build this assembly completely before attaching it to the tank with
silicone.
Finally, two shelves need to be attached to the tank wall, directly
opposite from the two shelfs on the acrylic partition.
Now you need to build the drip-tray. This starts with a 1/4" piece
of acrylic, cut to fit the bio-ball compartment. It must rest on the shelves
at the top of the bio-ball compartment. You should size it so it's got a little
wiggle room, to make it easier to get it in and out of the sump. Then you need to
cut four strips to make up the "walls" of the drip tray. You want water to collect
in the tray, and be forced to go down thru the holes in the drip tray. Cut the
four walls, and attach them using acrylic adhesive. At this point, the tray
should be water tight. Then drill SMALL holes (1/16") spaced 1" apart, over
most of the drip tray. Leave the center section of the tray un-drilled. This
will force water to spread out, giving a more even distribution of water over
the tray. After the wet/dry is completed, you might find you need to enlarge
the drip holes, but if you make them too big initially, all the water will go
down thru very few holes, reducing the effectiveness of the trickling.
The last step is to cut a piece of "egg crate" to fit the bottom of the
bio-ball compartment. Egg-crate is the plastic gridwork often used in
commercial flourescent lighting fixtures. This just supports the bio-balls,
and allows the water to flow thru into the sump.
All of the parts and partitions should be below the plastic lip on the tank.
This will allow you to cut acrylic covers to go over the wet/dry. Covers
are important for two reasons. First is noise reduction. Second is to
keep dust/dirt/insects out of the wet/dry. I made
my cover in three parts. One part covers the drip-tray. It has a hole cut in
the center, with pvc fittings to connect to the hose bringing water from the
overflow box. The next part covers the pump compartment, and it has a hole
cut in it for the return hose from the pump. And finally, I've got a
seperate cover in between the other two. My wet/dry is actually longer
than the picture, so this cover is almost the same size as the drip-tray
cover. Cut a notch in the center piece for the wires for the pump
and heaters, and anything else you stick in there.
I hope this information gives you a general idea how my wet/dry is
set up. I'll be adding more info as I have time. In the mean time,
feel free to email me with any questions.
Special thanks to Bob Odenweller, who actually did most of the work
on my wet/dry. I would have managed to screw things up nicely
if it wasn't for his expert guidence and skill.
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Your feedback on this article would be greatly appreciated. All feedback is
anonymous, so please, be honest. Your input can help me create better content.
If you have any questions about this article, or if you feel that something is
incorrect or missing, please let me know via email at cgadd@cfxc.com
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