I have an Aquarite. It does the same thing when generating. Small bubbles come to the surface and you can see what appears to be a very fine "cloud" coming from the returns. I put a filter sock in front of my return when I first noticed (same as you, only 2nd year and first time I noticed it happening) - I thought it might be DE. All I trapped was lots of bubbles - they increase dramatically when you put something in the flow.

The bubbles are hydrogen produced by the generator. I guess there are lots and lots of tiny bubbles, thus the cloudy appearance, and a few bigger ones that actually look like normal bubbles!