[Maverick00]

my cpr doesnt have the grooves your talking about but i try to keep the water level just above the intake so the surface of the water gets skimmed but at the same time doesnt create turbulence and produce air bubbles/pockets. It takes some adjusting to find what works the best. I found I have to keep the prefilter sponge at the back of the cpr as clean as possible (wash it every few days). If i dont the water level in the tank will slowly creep up as it starts to clog with debris and create more resistance for the water flow.

Added: Im using two pvc ball valves, one to limit the return pump, and one to limit the cpr outlet. That will give you full control of the intake and outtake. It was recommended to me in a previous post and has worked great.