"Pszemol" wrote in message
...
"swarvegorilla" wrote in message
...
Yes, yes I do.
contact time is very important.
water blasting thru media too fast will not allow
bacteria sufficent time to eat nutrients in the water.
[...]
but biological filtration occurs best slowly
delicate colonys building on top of each other
forming matts of brown crap
charming I know
should visit a sewrage farm some time
will be quite the bacteria eduaction for you!

Sewage farm and aquarium filter have big difference:
Sewage is pass through, water passes one time only.
Aquarium filter works in closed circuit loop...

And this single difference is very important!

When you have single pass filter - then yes, you
want long contact time for the bacteria to use up
all the nutrients from water and leave water pure.
When you have closed circuit loop, like in the aquarium,
it does not matter really if you put 10 gph through
the filter or 100 gph the if not all nutrients
will be removed in the first pass, than you have
10 more chances - the same water passes through the
filter several times per hour!

I would rather say contact time is NOT important.
What is important is that bacteria will have enough
oxygen in the whole volume of the filter media...
When you restrict flow in quest to get long contact
time you can make the last part of the filter
lack oxygen and bacteria will not work since
nitrification requires a lot of oxygen to consume.
On the outlet of the filter with low flow bacteria
will starve. We do not want this to happen.
We would rather give the filter maximum flow it
can handle to make sure bacteria in its whole volume
of its filtration media is well fed and oxygenated.

each filter is matched to flowrate
and no, every sewrage farm is not an open system!
infact most are closed too!
you have missed the point friend and it's too late and my chicky is too hot
too explain now.
later tho