40 gal filter for a 20g?

i would suggest the HOB rated for a 40 gal ... i rather have it over filtered than under any day

for hobs you want to shoot for 10x/hour filtration so youd want 200 gph on a 20 gallon tank


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The tank size rating on filters is pure nonsense. Never believe it. I usually put around 60 gallons of filtration on a 20 if you're gonna put it in their terms!

Mount_Prion said:

The tank size rating on filters is pure nonsense. Never believe it. I usually put around 60 gallons of filtration on a 20 if you're gonna put it in their terms!

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+1 I usually go by the gph rating if it can over turn a 20 5-10x an hour is good. The more over turn an the better.


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Yes


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You want to dissassociate the whats the filters rated for and what size tank you will actually be puting it on. Focus on gallons per hour (GPH) of the filter. Like others have said, shoot for 10x turnover rate of the entire tank per hour.

A standard filter for a 20g tank is probably 40-50 gph.
That means your only getting 2.5-3x turnover rate in the tank per hour; not sufficiant.
So, you would want to look for a filter thats was around 200gph to achieve, atleast, what is generally accepted on this site.

I've had an AC70 on a 20 long for about a year without any problems.