You need to do a bit of reading about the issues people have had when they have located their CO2 a long way from the tank. I think when they first just throw the system together they end up with completely uncontrollable CO2 bubble rate, ending up with nothing, too much or cycling between nothing and too much.It's either going on a shelf behind the tank or in the cellar top with a chain around it and then just drilling through the wall. Both places have pros and cons
I think the issues is long lengths of CO2 tubing pressurising and depressurising, along with diffusers causing oscillating CO2 supply.
I think you need cylinder -> regulator -> solenoid valve -> the long connecting length of CO2 tubing from cellar/garage -> needle valve -> one way valve -> bubble counter -> diffuser.
The bits in green need to be as short as possible, any long lengths of CO2 piping in this areas causing issues. You might also want to consider the "long connecting length of CO2 tubing from cellar/garage" being made from something tougher than standard CO2 tubing, people have used copper pipe as well as 4/6mm rigid plastic pipe.