It appears this is the overflow line from the display down to the sump? If so your sump should have sufficient baffles to dissipate the bubbles before they reach the return pump chamber. Do you have over-under-over or under-over-under type baffles so the water must change directions and give up the bond with the bubbles so they travel to the surface and pop?
In the picture it appears the sump level is quite high, are you baffles high enough so they work as intended or are they all submerged? Do you have sufficient room in your sump to contain the backflow when the power goes off or if you shut the return pump off for feeding or maintenance? This can be critical.
Again a description of your plumbing, pump and sump arrangement would go a long way helping others troubleshoot your system. I am not a fan of filter socks, bags or foam/sponges of any sort and do not use any of them myself. They trap detritus and can cause more problems than they help if not kept clean. I hate anything that requires maintenance or attention, I want things as simple and troublefree as possible.