# How can I measure the actual throughput of my filter?



## twoheadedfish (May 10, 2008)

I have an in-tank fluval filter that's on the fritz and I want to know how long I can go with a semi functioning filter. it's consistent, but underachieving.

so, i figure, since it's over rated for the tank as it is, if i can measure it's current gallon per hour throughput i can take a pretty educated guess as to how long I can put off replacing the filter.

trouble is i have no idea how to do this.

non-English majors, i'm looking at you.


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## ameekplec. (May 1, 2008)

Ideally:

Connect some kind of tubing over the output so you can have it flow out of the tank.

Then drain it into a container that you know the volume of, and measure the time it takes to do so.

The plug it into a simple equation, and tada! you have flow rate in gph.

flow (in gallons per hour) = (volume of container in gallons) x (3600 / # of seconds to fill container)


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## twoheadedfish (May 10, 2008)

that....was simple.

thanks!


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## Riceburner (Mar 14, 2008)

I was gonna say that....really..


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## twoheadedfish (May 10, 2008)

oh lord....100 litres an hour down from 700. sigh.


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## ameekplec. (May 1, 2008)

Have you tried to clean everything (media, prefilters, impeller housing)? That usually recovers some functionality.....~25gph wouldn't even classify it as a filter for a nano tank.... 
If you clean it out and it recovers, then good on it. Otherwise, I think it's time to bite the bullet, and go for a new one.


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## twoheadedfish (May 10, 2008)

Yeah. i've cleaned everything and replaced the impellar.


just did a water test and things look good. i've been doing small water changes daily.

filter tomorrow. at least it's an excuse to get to the lfs


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## Ciddian (Mar 15, 2006)

Keep this in mind. When i worked at big als we had all been standing around talking about GPH and it was brought up that the output is rated before the actual filter materials are in there. So...what you buy isnt exactly what you get i guess.

I am not sure if this applies to all filters or am I sure of which one, its just interesting if its true.


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## ameekplec. (May 1, 2008)

Actually, it is true. All filters are rated with no media in them at all. So after actually adding media and such, you lose a fair bit of efficiency

That being said, with canisters, they probably rate them at 0 ft (so not having to pump against gravity), so that probably also contributes to a decrement in filter flow.


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## planter (Jun 9, 2008)

ameekplec. said:


> Actually, it is true. All filters are rated with no media in them at all. So after actually adding media and such, you lose a fair bit of efficiency
> 
> That being said, with canisters, they probably rate them at 0 ft (so not having to pump against gravity), so that probably also contributes to a decrement in filter flow.


Not all filters will reduce flow with media. I'm not sure how those filters work as I have never used them. But this is an interesting read. Perhaps you can modify yours as well.

www.plantedtank.net/forums/equipment/63687-eheim-2215-2217-facts-diy-performance.html


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## ameekplec. (May 1, 2008)

Actually, yes all do. 

If you read that post carefully with which you refer to (which I have seen before), that part about them having the same output is AFTER media (notice the actual output of open/spray bar is LOWER than the advertised output; the 2217's advertised flow is 264 gph, and the closest to that is 229 gph, more than 30 gph under the advertised flow rate), and refers to the output of each model vs each other when the stock 2215 impeller is replaced by the 2217 impeller.

It's a simple matter of boosting performance numbers and shear stress and turbulent flow, both thanks to fluid dynamics. 1. Companies advertise the empty flow rate to make the filters seem like they pump more than they will do when actually used with all media, and 2, If you put anything in the filter it will cause some disturbance in the flow and cause turbulent flow which will decrease filter output.


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## BillD (Jun 5, 2006)

If the flow isn't reduced by adding media, I would wonder about how much bypass is occurring, which was not considered in the test piece.


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