Really depends on your rockwork - I find that the gyre creates a heck of a current at the top and bottom of the tank, but the center can be lower flow depending on the crags, nooks, crannies and caves. That said, any flow opposing or interfering with the gyre will cause an issue with the gyre, slowing down the water movement. Id say that if you have good flow, but a spot that you want higher flow through, or a ledge or outcropping that kills the gyre movement, an additional pump maybe justified. Easiest way to figure it out is to run it for a while with the gyre, look if you need more flow and adjust accordingly.

