Planted Tank Guru
Join Date: Nov 2009
Location: Missouri united states
I think much of the suggested flow for your tank/my tank is due in part to drop off in gph rating from some/most filters after they are packed with media, and become dirtier between service.
Fish load definitely ,and waste created daily also plays big part.
You can only filter what is floating about in the water column so good flow keeps the material you want filtered out in suspension longer, as opposed to as mentioned,just falling to the bottom where no filtration can remove it.
Opinion's will always vary on this topic.