# Re: filter flow rates

```On Tue, 28 Dec 1999, Roger Miller wrote:

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

The formula Tom gave:

snip<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>snip

The formula is right on the money (The only difference in the one we used in
testing in chemistry was the purity coefficient was rated at 12.755, but hey
close enough) Take the following example: You have a 55 gallon aquarium with
a 400 gallon per hour filter on it.  Using your math, it would follow that
that water in the aquarium would be filtered 7.27 (rounding here folks) times
per hour.  If we use the formula on the other hand, we find it takes 1.75
(rounding again) hours for the water to be filtered just once.  That is some
difference.  The USC chemistry class did a study mixing different substances
into the water columns of different aquariums and then filtering them out.
The formula Tom gave was (practically anyway) the same one we used and
verified by our experiments. Alas, that was many moons ago and I no longer
have the papers in front of me as proof.  But do not despair, for there is a
wonderful book out there.  It is called "Aquatic Systems Engineering: Devices
and how they function" by P.R. Escobal. The book explains the water turnover
rate much better than I could ever hope to.  One place to get it on-line is:
www.petsforum.com/twolilfishies, item #159 under books.  It is kinda pricey
at \$29.95 plus \$5 s/h, but worth it if you got to know how it all works. I am
not connected to petsforum or the book in any way, just thought some might
care where to get it.  Hope this helps.

James Watford
Columbia, SC
```