I've just filled the laser tube for the first time in my DIY laser. It's an EFR F2 80W. It says the flow rate can be as low as 2 litres a minute and I just measured mine at 2.6l/min so I assume ok. However, there is a bubble in the glass tube and it's not moving. There are loads of really tiny ones too but I'm guessing they will dissapate in time. The laser tube is level as directed by the EFR installation details. I could probably adjust to give it a very slight uphill in necessary. The thing is though, do I need worry about the bubble? I have attached a photo.