Fwd: Bio Tower

This mail came to me from Christopher Holloway
   (Christopher.Holloway at hr-m_b-m.defence.gov.au)
who has a problem posting it to APD.

Here goes...

I read your recent post in APD re: biotowers. I have difficulty in
successfully posting to list
so tend to use personal e/mails; hope you don't mind.
For the biotower, the rule of thumb is that the amount of filter media
should be equivalent to 10% of the tank volume for saltwater tanks and
about 5% of the tank volume for freshwater tanks. These are minimum
figures; a larger quantity of media would be quite okay. 

However, I spoke to someone in Belgium a little while ago who said that
the volume of the filter should equal the volume of the tank but all
this means to me is that he had very small tanks -  1400 litres of water
(as would be your situation if you follwed Alain's advice) is a pretty
serious amount of water, especially for you floor to cope with. 
For a 700 litre tank, then - if it's freshwater, which I assume it is -
you're looking at having at least 35 litres of filter media. If you're
thinking of using oviflow or bioballs or something similar it will
probably take about 5 seconds to realise that the outlay costs are
pretty high. One advantage however is that once you've got them, you've
got them for ever. As an alternative filter media (and here I'm assuming
you're going for complete biological filtration) you can use filter mats
in addition to bioballs - the mats look like masses of fishing line
compressed into a mat about 2 cm thick, or shotgun wads (much, much
cheaper and fairly good for surface area).
As for the size of the biotower - you'll just have to experiment. Buy
the filter media first and then build a mock-up of the filter out of
cardboard. Keep mucking around with it until you get the right
dimensions. This may sound like a bit of work but believe me it's less
expensive and considerably less frustrating than jumping straight in,
building a sump out of glass or perspex or whatever and finding that
it's the wrong size or shape etc. I'm not sure whether you want to have
the filter under the tank (what I know of as a sump filter) or in some
kind of drum next to the tank or outside the house or whatever, but this
will also affect the size and shape of the filter.
Other considerations that come to mind include the method you plan to
use to move water into the sump (overflow or siphon), the sort of
pre-filter you might be tempted to use and the flow rate through the
filter: you want to turn the tank over at least twice an hour; four
times an hour is obviously better and a pump that moves 2800 litre/hour
is not that much more expensive than one that moves 1400 litres/hour. 
Ps - it's often cheaper to use an agricultural pump for this kind of
application but make sure, if you do go this route, that you get a pump
designed for continuous running - most ag pumps are not. An Australian
company called Davey makes a pump designed for pond filtration - I can't
remember the model number but if you want I'll chase it up. Otherwise
consider a Hozelock pump - expensive but worth it or, of course, an
People on the APD might like to comment on this so feel free to post it
to the list. 
Hope this helps,