Internal filter going at 1/3 of the speed

fabiobruno

AC Members
Oct 3, 2009
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Bristol (UK)
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Fabio Bruno
I recently had some minor issue in my tank (see http://www.aquariacentral.com/forums/showthread.php?t=225437) and almost by chance I decided to check the water flow from my filter (Fluval U2, I strongly recommend this filter!).
The flow rate from the specification is 400 Lt/h, with some simple math this equate to 1 lt every 9 seconds.
I plugged a pipe to the filter and measured the time required to fill 1 Lt.
28 seconds at the first check!!!!
I removed all media, cleaned the filter, the impeller (that I had cleaned up just 1 month ago), checked without media and measured 17 seconds to fill 1 Lt.
Media back (reasonably clean) and now it takes 25 seconds.
To cut the story short I went to the dealer and got the faulty filter replaced.

Now my question is did anybody ever experimented this? I was expecting a filter to either work properly or stop all together (and OK the media clogged may slow down the flow considerably too, but this wasn't my case).

Is it possible that the motor just partially break? Because this could explain the issue... I went on holiday 3 weeks ago for 1 wk. I attached the auto-feeder and I had to slid a bit the lid in the canopy to allow the food to go in the tank, this left an open 10x10 cm square hole in the canopy that let some water evaporate in the week. The day I came back the tank had lost ~2 cm of water and the filter was catching some air so the water flow wasn't homogeneous. I added the missing water and everything seemed OK.
Now since a friend had checked just the day before I guess that the filter struggled for 24 hours max. Could this have triggered the problem in the motor ? As I said at that time the filter seemed OK, then yesterday I noticed a slow flow.

I'm wondering if good filters have some sort of protection to avoid the motor to stop working all together...

Anyway I thought this was a story worth to share.... If something sadly start to be not spot on in your tank you may want to check your filter.
 
I don't see howa 2 cm evaporation issue would affect the filters performance, but then I don't know how you have it placed in the tank.

On another note, most any filters gph is extremely over rated and often is the flow of the pump discharge in testing...not the actual flow of the filter with all the media and restrictions in place.
 
Hi Bob, that filter can use a venturi system, but in this case the filter top needs to be 1 cm above water level.

I can imagine the figure used is the one without media, but even though the water was flowing at half of the speed.
To be honest I didn't check the new Fluval I've got in exchange but visually was much faster. But I did test my spare filter to cross check my method, that was rated 450 Lt/h and was filling 1 Lt in about 8 sec, that is about right. However I went for the Fluval again because much quieter and much more effective, the 3 stage filtration system really makes the difference.
 
the pipe will also cause back presure and the pump won be built to deal with this and IME this can have huge drawbacks on perfomance
 
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