Here is an easy way to block light into the over flow units and an additonal place to mount several fans for additional cooling in the hood. 1- one piece of black acrylic 3/16" thick bent by supplier at a 90 degree with 3 1/2 inches by apprx. 9 inches and 12 inches wide (these measurements can be made to suit). 2- 1 foot of clear acrylic 1/2" bar stock 1 inch wide. (enough for 2 guards) 3- acrylic glue (preferably thickened). -cut the edges of the the longer part of the black acrylic at a 45 apprx. three inches both ways and keep the triangle pieces cut off. -drill at least two holes in 3 1/2" part which will attach to the hood. -Cut two pieces of 1/2" bar stock 3" long for each cover. -Take the large angled black acrylic piece and round off the front corner edges where the pieces were cut off with a sander. (belt sander on table. by hand, etc. just sand the cut into a curve as needed to your liking) -glue two of the 1/2" bar stock 3" long onto the bottom of the black acrylic cover posistioned to sit mid way on top of the over flow front lip at apprx. the 1/4 points or as desired for support. -glue the triangle pieces that were cut off to the strenthen the back and curved bend in the acrylic. (position so that a full contact is made at the 90 degree bend. once glue sets sand off point that hangs over in back to match the bend. -once glue has completely set up mount the cover, level and install two stainless screws to hold the unit in place through the vertical 3 1/2" acrylic back and tighten. NOTE: you can now mount a fan or two on top of the covers and direct across the water for additional cooling. all that needs to be done is to use aquarium silicone to glue the fans down so you can replace them should they fail. following are several pictures that will help. this project is designed for a hood that has a backing for support of the cover.(fully enclosed etc.) TIP: The cover should hang over the overflow apprx. 1" all three sides.