Knocking out the teeth on overflow?

[Aquattro]

Mason, I have had overflows with no teeth, but snails often made their way into the plumbing. This is bad. I then fashioned a grill inside the overflow box that worked fine.
My current overflow has slots 1/4" wide, 1/4" apart and 1-1/4" deep. It handles the flow of the MAG 12 fine. It is a 6x6 box. Are you sure it's the grill and not the plumbing? What size piping do you have?