reeffreak
Reef pro
Same principle as having only the overflow gills at the top.Once water gets below the gills on the top parts,the flow stops.I've done several test with the power off and the sump only fills additional 2-3 inches.
I'm planning on ordering live rock from Live Aquaria too. But their "large" Fiji rocks... It's $3/lb including shipping, can't beat that.