Re: Size of bio-tower

> From: Zon Hisham Bin Zainal Abidin <zon at mad_scientist.com>
> Date: Sat, 07 Dec 1996 23:45:06 +0800
> Plan to set up a 700 litres tank using trickle filtration.
> How do I
> 1)determine the volume of water the sump should have?

The larger the better.  A couple of things are important. 

With a typical trickle filter setup, the water level in the tank stays
constant and the water level in the sump will vary as water evaporates
or is added.  When the water level in the sump gets to a certain low
point, the pump inlet will start a vortex and begin sucking air.  I
like to keep the water level a couple of gallons above the sucking
point so that I don't have to top off the tank every day.  Our closed
top tanks lose about 1/2 gallon per day; the open top 120g tank loses
1 gallon per day.  We live in a very dry climate.

You will have to experiment to determine how deep the water has to be
to avoid sucking.  It depends on where the water inlet is positioned,
the shape of the water inlet, how fast the pump pumps, etc.
Also, you don't want the water level in the sump to be too high.  It's
better (but not necessary) to keep the biomedia out of the water, so
that is one upper limit.  Also, when the pump is turned off (for water
changes, maintenance or when the power company screws up) some water
will siphon back into the filter.  The skimmer will continue to drain
water until the water level is at the bottom of the slots and the
water returns will back-siphon water until the water level is below
the siphon break holes or the (usually unnecessary) checkvalves kick
in.  The sump has to be large enough to contain the extra water that
drains back in this case. 

A bigger sump is better because the system then contains more water so
the "inches of fish" can be greater if that is a concern.

> 2)determine the volume of the chamber that holds the bio-balls?

Depending on the surface area of the media and the bioload in teh
tank, somewhere between 5% and 20% of the tank volume is a good rule
of thumb.  We use Dupla BioKascade media and have 15 liters of media
for 300 liters of water.  We have a fairly heavy bioload.