right corner, the film at the surface is preventing the bubbles from breaking open, it's like a natural oxygen reactor, allowing them to dissolve completely
Cool pics Konrad. Mine produces similar amounts, how long after your lights on does it take for your first plant to pearl? I think my record is 20 minutes but I'm only on 1.8 WPG at the moment. After two or three hours most of mine are producing bubbles and I get the same effect as you on the surface. I'll post some pics later.