How big is your display tank? How much drain down water (the water that runs back down to your sump when you turn off the return pump or lose power) do you need to account for? A 10 gallon tank does not give you much room for error, particularly if you have a refugium in it. I size my return pump section large enough to accommodate all the drain down water, if you don't then the water level in your refugium will rise when the return pump is off, your macro algae is likely to float over your divider and then when the pump turns back on it will suck algae into your impeller. You also could risk a flood if the drain down water has a greater volume than the space available in the sump. If the design shown does accommodate all the drain down water it is a good design.