nanostream mods?

[Dorado]

I have a couple of tunze nanostream 6055's that are located a couple of inches below the water line. It doesn't constantly happen, but maybe every five minutes one of the powerheads makes a vortex sucking in air and spreading bubbles all over the tank. An easy fix would be lower the pumps, but because they are located in the front of the tank, I don't want to do that. I'm wondering if anyone knows of a mod/shroud that would work to alleviate this problem.

 

[Stigigemla]

A sheet of something floating at the water surface over the pump will inhibite the vortex.
I have used 1/2 inch frigolite held on place with a little fishing line.