I use barrel filters and the water can drop 6" without a problem.
Since the bottom drain is plumbed into the side of the first barrel
that is as low as the pond water level can be pumped out by the pump.
If you wish to use a filter like you describe you might want to run a
water line and hook up a constant level switch for your pond. If you
have chloramine in the water that brings up another problem.

Regards,

Hal

On Sat, 8 Feb 2003 11:30:30 +0100, "Pierre de Ponthiere"
wrote:

I agree completely with your explanations when the connection is "bottom to
bottom".
But a lot of filters like Clean Pond 12 described at
http://www.verhaertnv.be/pdf/8A.pdf have the rim of the first vessel 1 or 2
inches below the maximum level. (The second vessel is filled by overflow of
the first one thru a vertical slit visible beteween the the 2 vessels). It
results that the pond level has to be maintained constant which can be a
problem during vacations...

I disagree with several of your cons to a bottom drain.
snip
Con's
Potential leakage of pipes below the ground level
If the pipes are properly installed and of decent quality, this should
never be a problem.
Maintain the pond waterlevel in strict limits
My water level can vary 15" without it being a problem. It comes down
to proper design.
Winterizing, probably more difficult.(how to empty the pipe comming from the
pond, even with a valve the upstream water could freeze)
I live in northeast Ohio where we routinely have stretches of zero and
even sub-zero temps and have not had any problem. I just keep a 25
watt bulb in the pump house to keep the temp above freezing. The pump
house lid has a piece of 2" foam insulation.

More difficult to install
Yes, but this is a one time labor, however, it eliminates a lot of
future work cleaning the pond.

"Pierre de Ponthiere" wrote:


2) Pump in the pond
Pro's
Easy to install
No leakage below the ground level
Empty pond by pipe leakage avoided with a flottating switch in supply
electrical line
Pond waterlevel is not critical
Safe winterizing if all pipes (above ground level) are emptied before
freeze.

Con's
Pump hashs the dirt sent to the filters (New designs of Vortex pumps reduce
the problem?)
Settlement vessel will not work properly -- install brushes in its
More maintenance: purge the settlement vessel and clean the filter pump,
clean the brushes,..
Difficult to hide the bio filter (filter put on the ground)

Cons:

pump that can pull in solids (say up to 3/8 inch for example), will pull
in plants and things like leaf stalks, and plug up the filter.

You can limit that by installing a pre-filter, but then you need to
clean it.

With a pump in the pond your gonna have to pull it out and clean it
periodically, at best every few weeks.

this has been my experience.

My prefilter only needs cleaning every 3-4 months.
It is a milk crate. Open end is down.
Exit pipe is up through center of bottom.
Wrapped with two layers of fiber glass screen
on four sides and bottom of crate.
To clean I lift out the whole thing and spray with
a water hose.


--
D. Wain Garrison
If you can read you can learn anything, for
there are those smarter than you who can
write, however, not everyone who can write
is smarter than you.
"John Hines" wrote in message
...
"Pierre de Ponthiere" wrote:


2) Pump in the pond
Pro's
Easy to install
No leakage below the ground level
Empty pond by pipe leakage avoided with a flottating switch in supply
electrical line
Pond waterlevel is not critical
Safe winterizing if all pipes (above ground level) are emptied before
freeze.

Con's
Pump hashs the dirt sent to the filters (New designs of Vortex pumps
reduce
the problem?)
Settlement vessel will not work properly -- install brushes in its
More maintenance: purge the settlement vessel and clean the filter
pump,
clean the brushes,..
Difficult to hide the bio filter (filter put on the ground)

Cons:

pump that can pull in solids (say up to 3/8 inch for example), will
pull
in plants and things like leaf stalks, and plug up the filter.

You can limit that by installing a pre-filter, but then you need to
clean it.

With a pump in the pond your gonna have to pull it out and clean it
periodically, at best every few weeks.

this has been my experience.