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RE: Filtration questions

In APD #916 Hugo Hoekstra responded to Edison Yap's question on filtration. He

Hello Edison,

>I would like to ask the following questions regarding filtration:

>1.  Is it okey to use an Ehiem 2213 Power Filter ( for 66 gal tank) for my
>100 Gal tank with around 10 Dwarf Cichlids , 20 Tetra, 20 Yamato Ebi, and
>some 5 SAE?

Hugo responded by saying:

"It's on the low side I think, I am using an Eheim 2215 for my 100 gallon
tank, and this filters the water twice an hour."

I agree that this is on the low side but according to "Aquatic Systems
Engineering: Devices and How They Work" by Peter R. Escobal the statement
"this filters the water twice an hour" is not correct.

When water is filtered it is introduced back into the non-filtered water. The
ratio of non-filtered water will gradually decrease as the filter is run. 100%
of the water will never be totally free of contaminents as pollutants and
particulate matter are always being introduced into the aquarium.

The rating of any given filter is for maximum gallons per hour with new
filtering elements. As the filter becomes clogged with detritus and other
contaminants the flow will be depleted.  In this book Mr. Escobal gives a
formula to determine the average turnover rate of a filter. He defines
turnover rate as "the duration that all water in the tank is filtered to a
specified percent in purity".  You cannot just divide the gallons of any given
aquarium into the filters rated flow to determine the turnover rate. The
formula is: Tavg.= 12.75xG/F.
Tavg = Turnover rate (average)
12.75 = given number (purity coefficient)
G= Gallons of water
F= Filters rated flowrate
Using this formula, Edison's Eheim 2213 and his aquarium will have a turnover
rate of 10.2 hours.
Tavg = 12.75 x 92.8 divided by 116
92.8 = water capacity of 100 gallon aquarium (using George Booth's formula).
116 = Eheim 2213 advertised flowrate.

Using the manufacturers recommendations for tank capacity the turnover rating
for an Eheim 2213 is 4.4hrs.  Tavg = 12.75 x 40 divided by 116

Using this formula for Hugo's Eheim 2215, the turnover rate is 7.4hrs. 
Tavg = 12.75 x 92.5 divided by 75

The turnover rate using the 2215's manufacturer recommendations is 6hrs.
Tavg = 12.75 x 75 divided by 75.

Turnover rates for a net 100 gallon aquarium:
100gph = 13hrs
200gph = 6.5hrs
300gph = 4.25hrs
400gph = 3.25hrs
500gph = 2.5hrs

BTW, this book contains additional information on heaters, reactors, skimmers,
UV sterilizers, airflow, ozone, pumps and hydraulics. There are charts,
formulas and diagrams to determine rating needs for all the equipment covered.
The author, a former aerospace engineer who contributed to the Apollo program,
is the founder of Aquatronics in 1969 and Filtronics in 1971.

Sorry for the long post.

Tom Bates
Allentown, PA