In the Cad39G water overflows are located in 2 locations. On the far right water flows into chamber 1 which in my case houses LR and a few bioballs. I added a sponge filter in this compartment to minimize the waterfall sound. It worked well from day 1 with the sponge siting directly on the top of the bioballs and wedged nicely into the space.
The 2nd overflow is in compartment 3 which is also the refugium. Due to the design there is about a 4-5" water drop and the waterfall sound was too much. I tried installing more sponges but the force of the waterfall dislodged them.
So I built this waterslide device from some plexiglass. It wedges in and hangs on the back glass. The light unit and skimmer were removed for installation.
But as you can see there is still a small waterfall at the rear of the water slide. So I added an extension to the hanger until the rear end of the waterslide actually sits below the refugium water surface.
But I was still getting microbubbles so I added a small piece of sponge to the waterslide under the skimmer exit and that seems to do the trick. Now I have an almost silent water flow and most of the microbubbles are dealt with.
The bar that you see in the above image is the refugium light. My next step is to adjust it until enough light enters the refugium to make it effective. The light may have to shine in from the back of the aquarium to ensure enough light gets in. That will require some testing.