Does the tank have a sump or is it a cansiter?
Most large LFs tanks use sumps.
There is a different design, it's actually easier to make than the in line type and has no backpressure at all.
I'll do a pic series of it on my site in the public section.
It's very easy to make.
The flow pattern from the output of any CO2 reactor or sump return is critical on larger tanks, the CO2/return water needs to be evenly and rapidly distributed throughout the tank.