The green leaf aquatic one right? What size are you using, since there seem to be different options.
And this might be a silly question, but the inline should be connected to the outtake tubbing and not the intake right?
Also, if you had the time to look at my 75 journal that'd be grand, because I'm not sure which filter would be better to connect this too, the right side or the left? Left already has the heater but I'm not sure if that matters.
I'm using the largest size because it has to be about the same size as the tubing coming out of your filter - mine is 16/22mm
Yes, place it on the output of the filter - Pushing CO2 into a filter could cause lock up and other bad things for the bacteria in the filter. Plus it would get dirty really fast.
I have one filter with an inline heater and diffuser - They are both ceramic tubes with no baffles or reduction in tube diameter so they have no adverse affect on flow - it's a straight, albeit longer, shot to the tank.
I have mine set up so the water churns in a circular fashion. The filter output pushes from one side to the other and then the Hydor nano pushes it back towards the filter intake.
You can put it on the side closest to the korelia that pushes water across the tank so it disburses the CO2 better.