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Building a
giant plywood tank
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| I received
many additional questions (many thanks for that) about building a
plywood tank since this article is online. After getting more
experience with this kind of material, I wanted to change my intro
text though, mainly because my initial enthusiasm has faded a bit.
YES these tanks cost less, and YES they weigh less, but the first
point is rather relative, as a sub 1000L glass tank won't break
your bank account. What's more in my opinion, is that the aquarium
as such only represents a tiny piece of the total cost to get it
up and running as it should, with all fish, filter & lightning
included! The weight argument is also of minor importance with a
permanent tank. So what remains of the enthusiasm? If you're
rather handy, this DIY project can give much satisfaction and joy
if it's done right. I also hear you readers coming... am I going
to build more plywood tanks? YES I'm indeed going to build more
plywood tanks, but this time I won't use precoated plywood, as I
discovered that the waterproof layer turns out to be the weak
link. Punctures occur very easily, as the mechanical resistance of
the protective layer is very poor. My next tanks will be made of
bare plywood, covered with a strong polyester - fiberglass
coating. This will guarantee a rock solid and a 100% leak free
construction that will last for a very long time! Still I feel
that the actual article should remain online unaltered, and when I
decide to make another plywood tank I'll simply write another
article about that project! |
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The giant ready to be filled for the first time. Notice the 75mm
drain pipe in the right corner for the water returning back into
the tank after filtration. |
What kind
of plywood did I use? Instead of using ordinary plywood that has
to be coated with polyester/fiberglass or epoxy after assembling,
I applied precoated plywood that is commonly used in the building
industry for framing reinforced concrete beams, columns, ceilings,
... as the smooth waterproof dark brown phenolic film coating
rejects all materials. Even glues and silicones don't attach to
it, unless the contact surface is sanded. The best quality boards
come from Finnish manufacturers, who produce a wide range from
*weather resistant* boards (film thickness 120g/m²) till *wear
resistant* boards (film thickness 400g/m²) These boards come in
various sizes and thickness: 1250/1500 x 2500/3000mm are the most
common boards available in wood shops and 18 - 21mm thickness is
also a good size for making tanks. Of course it's obvious that the
boards with the thickest film are the best ones for *aquatic* use.
More info can be found on the website of a specific Finnish
manufacturer. For more
information on the availability of such plywood boards you can
best contact your local wood shop. Also compare prices as you'd
probably don't want to pay more on a plywood tank than on a glass
one!
Good screws 5mm x 60mm or 80mm and polymer sealant are used to
mount the boards together. |
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After buying the boards with the correct dimensions in the
lumberyard, it's time to do some preparations. The contact surface
needs to be sanded a little bit wider as the thickness of the
board, and degreased thoroughly to ensure a good adhesive strength.
Take care not to sand off too much of the resin, as this exposes
the bare wood. In contrary to glass tanks, the silicones used for
building plywood tanks serve more as a watertight joint instead of
a glue joint. The real strength comes from long screws. The holes,
with a maximal distance of 10cm and 5 cm out of the edges, need to
be predrilled to prevent damages to the board. Be sure to use a
comfortable electric drill that enables you to dose force
accurately. Take some remainders to become accustomed to the
assemblage of such a tank, as this prevents you to have to buy new
boards after messing everything up. |
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| Of course
we put silicones between the wood boards before we start screwing.
Start with the bottom, then back, sides and finally the front, and
be sure to mount all sides against, and not on the bottom board.
The smallest bit of logical thinking will prevent many errors.
Glue the parts that are going to be assembled only a few minutes
in advance. Then start screwing gently while you watch out that no
board moves. After the first screw, an error still can be
corrected by removing it and start on another hole, but if you
discover you didn't work equally in the end, you can start all
over again with new boards. Use the silicones sparingly, as all
excess material that comes out of the joints needs to be removed,
what is a real messy and sticky job. When it's applied in a
correct quantity, the excess of silicones can be
spread in the inner corners of the tank with a wet fingertip to
serve as an extra leak protection. |
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Plywood strips as a front normally are
sufficient to keep the front window in place, but I used a
stainless steel frame for the front window, as
this aquarium is also a test case for my future
3780L/1000G kitchen tank. The stainless steel frame matches
the new kitchen design and it also doesn't
rust. Here you see how we've mounted the window. First we spread
the 2 tubes of silicones on the frame and then we put the window
against the bottom/back without touching the sticky stuff. Slowly
we let it come down, so the weight of the glass squeezes the
silicones gently to all directions. This way we get a huge contact
surface and we don't have to be afraid the window will ever
collapse. Before we can add water we also need to mount
transverse and length wood strips that will
prevent our construction from breaking |
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Here you see all construction details
in one picture: the low concrete walls and a black painted iron
frame that is accurately leveled with wood remainders. Right on
top is the plywood tank and the stainless steel frame with the
front window.
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Extra
advantages?
My Malawi cichlids appreciate the non-reflective dark sides, back
and bottom as they feel more relaxed with it, compared to the
reflective surfaces of most glass tanks with only the back covered
at best. A bare bottom plywood hospital tank is also better for
the same reason.
Large holes can easily be cut to mount plumbing and filters. Extra
accessories like filter hose clips can easily be attached on the
outside of the tank. |
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BEWARE: The same precaution has to be
taken to prevent damages to the bottom board as with glass tank
bottoms. Not that a plywood bottom will break, but the resin layer
can be damaged by sharp rocks, what can cause leaks in the long
term. Maybe it's the first time you read this, but that's why we
normally place rocks on thin Styrofoam plates. |
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