is 500 gph really 500 gph?

red devil

red devil

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Jan 7, 2003
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One of the most commonly asked questions I have seen posted on this forum is how much filtration is necessary. The crux of the question seems to be how many gallons per hour is necessary.

My questions:

Are the advertised stats on pumps what we can expect when we plop the pump/ph into our tank?

How does the rated capacity of the pump change when we add back pressure to it, i.e. connect it to a rugf filter, connect it to a homemade cannister or uv light, etc.
 
most decent reputable pump brands (Danner, LifeGard) supply a pressure/flow curve. The XXX gph number is at zero pump head. If the pump is situated 5' below the aquarium water level (5' of pump head), the flow will not be anywhere near the XXXgph stated on the label. Things like pipe restrictions, bends, kinks, etc. also come into play. a 500gph HOB filter will always produce 500gph, but a 500gph PUMP will only ever produce 500gph if you sit it in the middle of the fish tank so the inlet and outlet are completely unrestricted.
 
Any pump will have a varience based on the suction side pressure, the height (head) that it has to deliver the water, and flow restrictions caused by piping/tubing/UGF. Most pumps will have head/flow data available, but you will probably find just a value for a power head.
 
That is not true about filter flow rates. Most of them are based on the filter being empty- not even media. Once you put one on a tank and it begings to do it job, the flow rate will decrease accordingly. The dirtier the media gets, the slower the flow will be.

There is nothing wrong with makers using this gph standard just as long as fish keepers only use the numbers for nominal comparisons of brand new filters.
 
doesn't matter. i say however much these pumps are overrated by is cancelled out by the fact that your tank doesn't have as much water as it's known by.
 
No way.... you might lose 10-18% 0n volume, but once you add media, you lose 30-40% flow.
 
So...honestly, when people talk about how much the water is turning over in their aquarium...they are just numbers...and not actual rates. Maybe relatively speaking they are useful, i.e. 600 gph is twice as much as 300 gph but they are not "true" rates.
 
If you want to find out what it's pumping....you could always do a flow test.
-For a cannister
Use the outflow to fill up a container to a known volume and time it.
Ofcourse, you'd want to replicate height and distance from the pump, and use the same tubing/media. The main variable that would be tough to avoid is resistance. But even there, you could pump the water into a bucket that has the the outlet tube submersed into the same depth as your tank and measure the overflow from that bucket...and time it.

But all of that is only to double check a filter you already have, not very hand if you're researching for new filters. And as said before, it will vary with time.. i.e. algal restrictions in your tubing, and media buid-up.

Thats my 2 cents.
 
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