# Re: filter flow rates

```Rebecca;

There are a number of factors to take into consideration, among them are:

Manufacturers measure their filters flow with no media installed. As the
filter becomes clogged the flow decreases. When filtered water exits a
filter it mixes with unfiltered water. The filter constantly draws in a
mixture of filtered and unfiltered water. One can never expect to have 100%
of aquarium water completely filtered as aquarium water is constantly being
fouled by fish and plant waste. Realistically we can hope to maintain a 99%
filtered environment.

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

Tom Bates
Allentown, PA

>
> Date: Mon, 27 Dec 1999 09:28:46 -0600
> From: Rebecca Allbritton <rda3507 at acs_tamu.edu>
> Subject: filter flow rates
>
> "Tom Bates" <fish2r at netzero_net> wrote:
> >Subject: Re: eheim filters/CO2. sand substrate problems?
> <snip>
>
> > You cannot
> >simply divide the tank size into the filters rated flow to find the
turnover
> >rate. There is a formula that must be used.
>
> Hi, Tom,
>
> Why is that?
>
> Rebecca
> Bryan, Texas
>

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