Not sure what a stream rock is.The position and distance from the main tank really determines amount thats coming out the return.Either way this is for the sumps benifit and shouldnt be considered proper water flow for your tank.
well a the tunze stream rock is a rock that tunze pumps fit into. this isnt the return pump it is a powerhead in the display tank. im just curious to know if this means im pumping that much water into the overflow or am i just swirling the water around faster.
Nope. Powerheads simply swirl the water in the tank giving currents that fish like and corals need to live. The amount of turnover that you are providing your tank (the water that runs through the sump) is a product of the flowrate of your main pump (in the sump) minus any ineffieciencies (like height that you are pumping the water and any 90 degree bends in the piping).