Re: filter flow rates

On Tue, 28 Dec 1999, Tom Bates wrote:

> There are a number of factors to take into consideration[...snip]

> Here is the formula to compute average turnover rate. Average turnover rate
> is the amount of time, in hours, it will take for 99% of the water in a
> given aquarium to pass through a given filter. This formula takes into
> consideration the decreasing flow rates created by the filter media as it
> becomes clogged.
>
> T(ave) = 12.75 x G divided by F
>
> T(ave) is turnover average
> 12.75 is a purity coefficient (a constant factor [given])
> G is the net gallons of the aquarium
> F is the manufacturers rated flow of the filter

Sorry, but I have to disagree.  The filter flow rate divided by tank
volume is a good qualitative measure for filter sizing.

The average turnover rate is (under condition of complete mixing in the
tank) exactly the filter flow rate divided by the tank volume.  This
follows from rather intuitive logic and it can be shown with much more
rigorous (and pointless) math.  Some parts of the tank volume will cycle
through the filter more often than given by this ratio, and some parts
will cycle through less often; the average is given by the flow
rate/volume ratio.  I don't see how throwing a coefficient into the
formula adds to the usefulness of the ratio.

Roger Miller