- UPDATE FOR 2005
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Update for 2005
This photo was taken about June 2005 and shows some well
plants in the top of the bio-filter. These are still
in their pots to assist easy removal.
This year (Spring 2005) I have made a few changes to
my setup. I have found that Ziks design (click
here to see Ziks design) of venturi works very well
in the top of my bio-filter,
and it allows
frequent and easy cleaning of the venturi - something
I couldn't do as quickly with my own design.
Conversely I have found that my own design of venturi
works very well in the
pond itself (see further below).
Cleaning and Adjusting the Venturi
Having the piece of green scouring
pad as an air-filter is also necessary to cut down
the noise, because when its going it really makes
a good swooshing sound.
Every few days I check the venturi for blockages
from any muck that has come from the pump. I simply
green pipe out, and clean it off, making sure the
teeth are good and clean. I leave the pump running
while I do this (the water just overflows out of
the white pipe while I clean the tooth-pipe).
When I put it back together I insert the the green
pipe (making sure I've put the green side of the
teeth facing the side that the water enters, with
the white side of the teeth facing the way the
water goes into the bio-filter), and slowly push
it downwards until I see the water
suddenly kicks into action again.
I then adjust it for the most powerful draw on air.
I want a balance of allowing the best water rate
through, but also achieving a good aerating effect.
The trick is to listen!
Push the green pipe all the way down until it touches
the bottom, then lift it very slowly up
until the venturi effect starts to lose power, then push it back down a bit.
This allows the fastest water flow.
Now make a final adjustment by rotating the green
pipe very slightly to offset its angle against a
straight thru flow of water by about 10-15 degrees.
You will hear the swooshing sound become slightly
more intense, and this creates a swirling effect
in the bottom of the venturi which really mixes the
air into the water.
Tip for Adding Bacteria to your
You can insert
a funnel into the venturi pipe and then pour mixtures
directly into the bio-filter chamber. For example
a fresh bacteria mix at the start of the year,
or whenever you want to give it a boost. This gets
thoroughly mixed into the water passing through the
bio-filter by literally injecting the solution right
into its heart. This really helps jump-start
Silencer - Up Periscope
That venturi can sure make a lot of noise when its running!
And on a beautiful sunny afternoon when you're lazing
in the garden by the pond you just want to hear the sounds
of the birds, insects and water trickling lazily down
your stream. You certainly don't want to hear the constant
whooshing of your venturi.
So I constructed a better silencer than the simple wad
of scouring pad that I had stuck in the top of the venturi
hoze (photo above). Its a simple extension to the venturi
tube, which is a loose push-fit
over the top of the venturi hoze.
I sprayed it with green paint to make it blend in with
the plants. I call it my periscope silencer.
The periscope silencer is filled with some
green scouring pad cut and folded into a cylinder shape
so that it pushes into the 22mm piping. This scouring
pad acts like a baffle and helps to reduce the noise,
whilst also acting as a filter to prevent insects or
dust being drawn into the venturi. The black fitting
is a spare top insert for a bell-effect water
fountain, which inserts nicely into the scouring pad.
It doesn't have to be a tight fit. The idea is just to
give a cap to protect the opening of the pipe, and further
block the noise, while allowing easy airflow.
upright of the periscope is likewise filled with
fold of scouring pad. The whole periscope, with its 90
degree bend, scourer pads and the black plastic insert
all work to cut down the noise
dramatically, in fact so much that you can now only
hear the venturi if you are close to it.
Silence is golden.
Venturi in da Pond
This is my own design of venturi (originally described
Build a DIY Venturi
for a Pond Bio Filter page)
which I now use attached to a second Hozelock pump.
on a shallow shelf of the pond, just below the surface
of the water. It creates a tremendous swirl of air and
water, which the fish love to play in, and it creates
very good circulation in the pond. This in itself helps
keep muck and silt waterborne for longer so that the
main pump can send it to the bio-filter.
And here it is in action...... (ugh, look at all that
horrible slimy blanket weed, this was in the Spring before
the biological processes in the pond had kicked in
to reduce the algae).
It works on a timer to come on from 10am to 3pm to give
current, and oxygenate the water.
This particular venturi
was originally in my bio-filter, but then I changed
to the Zik design for my bio-filter,
and put my design for the venturi in the pond.
The Venturi in da Pond uses a Hozelock Cascade
2000 Low-Voltage (24v) pump (2000 litres/hour
or 0.55 litres/second).
Look at the photo and I'll explain a few points about
On the left of the photo you have the Cascade 2000 with
its standard pipe and valve fittings that comes with
the pump and normally feed a fountain and flexible hose
to other water features (2 valves).
The bottom valve controls
flow to the venturi pipe.
The top valve would normally
control flow vertically upward to a fountain head. The
valve is a simple butterfly
valve that is unable to shut-off fully, hence a piece
of cork in the top of the up-pipe to block it up completely
because the pump is quite a decent little fella and even
with the butterfly shut it would shoot a little spout
up the sides of the valve! Obviously I want all the power
to go to the venturi.
So the water passes to the right,
thru the venturi and out of a nozzle of 22mm pipe from
the T-piece used for
The bottom valve has a barb fitting which
flexible hose is normally attached to, so I have used
a short length
of black plastic 25mm piping which has a tight fit on
the barb, then the 22mm piping entry pipe of the venturi
is clamped into the black plastic tube using a jubilee
In operation I occasionally clean the plastic cage
around the pump which prevents too much crap from going
the pump, but I have found it performs satisfactorily
without cleaning for several weeks.
Venturis operate easier
the shallower they are, but oxygenate better the deeper
they are, so the strength
of the pump you employ will determine how deep you can
Obviously the small green air-intake tube (electricians
earth-wire sheathing) must be above water to take in
air, and if you were to put it deeper you might need
to rig up something to keep it at the surface.
works very well and my fish enjoy it very much.
it is often better to run a venturi at night because
that is when oxygen levels can drop, but I personally
feel that night-time is rest-time for the fish and they
probably prefer motionless water.
The choice of whether
you run the pump at night probably depends on how many
fish you have in your pond and therefore
how much oxygen they use up, and whether you have any
other oxygenation methods such as a stream, waterfall
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please contact me:
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