Thank you guys, I put a new safety wire around the tube and pulled it tight with pliers. It sat nicely, despite it looked different on the pic.
Unfortunately it didn’t help, still same amount of bubbles.
What I do next is exchanging the brass tube. Maybe I skip the soldered ring. Do you think it’s essential? I’m not used to that kind of tube connection.
I also will replace the whole inner Tygon tube. Should I ditch the brass tube inside the tank and use Tygon all the way?