Filter flowrate vs media volume

[kilnakorr]

Hi

I'm trying to figure out some relationsship between flowrate and media volume / surface area in canister filters.
Most filters have manufacters recommendations for tank volume, but media can be replaced with better media with much bigger surface area.
Question is, does flowrate really matter much, as long as suffucient bacteria can grow in the filter?

[Paul Sabucchi]

I am no expert, but have always preferred canister filters with a large volume of media and not excessive flow-rate vs ones that hold less media but with higher flow-rate. Someone over here (Italy) who has more specific knowledge reckons that a flow-rate through the media in excess of 15 mm/sec actually becomes counterproductive as the reduced contact time of ammonia/nitrates with the biomedia reduces effectiveness. Now you will ask how to work out the flowrate INSIDE the canister? Somehow it is the ratio between the pump flowrate and the surface area of the baskets in the canister but it would cost me a fair bit of headscratching to work out exactly how to work out the math!

[kilnakorr]

I am no expert, but have always preferred canister filters with a large volume of media and not excessive flow-rate vs ones that hold less media but with higher flow-rate. Someone over here (Italy) who has more specific knowledge reckons that a flow-rate in excess of 15 mm/sec actually becomes counterproductive as the reduced contact time of ammonia/nitrates with the biomedia reduces effectiveness. Now you will ask how to work out the flowrate INSIDE the canister? Somehow it is the ratio between the pump flowrate and the surface area of the baskets in the canister but it would cost me a fair bit of headscratching to work out exactly how to work out the math!

Thanks for the reply.
I'm not actually looking for any specific flowrate numbers. I'm just guessing that at some point the flowrate will be to low (or high) for the bacteria to thrive.
I guess that the answer I'm looking for is this scenario:

100G tank.

Canister filter A: 100 G/hr with 100 square feet bio-media.

Canister filter B: 50G/hr with 300 square feet bio-media.

Which would be the best option?
(Powerheads can be added for needed circulation as needed)

[bluelagoon]

Usually the larger the fish and more waste the greater the flow rate.Generally 4 x tank volume an hour.In planted tanks the lesser the flow rate.Any rate less than one times an hour is generally a bit too slow to oxygenate filters well.

[14Discus]

IMHO, more flow for aerobic bacteria and slower flow for anaerobic bacteria. My canisters are set up w a slow rate for anaerobic action. My hob has a high flow rate with my sump having a slower rate for the refugium and algae scrubber for nitrate removal. My flow into the tank is heaviest at one end allowing for more tranquil water at the other end.