233g, for dinos today and maybe forever lol. It's a 90w lifeguard uv. It'll need at least 1" piping. If I can mount the UV below the tank in the stand and run the pipe externally pulling water in I'll be able to do this in closed loop. My return line is only 3/4" and is the max size the tank is drilled for, so I'll not get near the 2800gph flow rate the mfg calls for, so I don't want to put this inline w the return pump. I'll be pumping about 40" upwards from the pump so about 1m if mounted in the stand.This thread is long and I admittedly have not read through it all. What size tank are you UV-ing?
I run 36-watt UVs at 400 gph through 3/4" pipe on 90-gallon tanks, and that kills EVERYTHING quite well.
I should stress that when you have that much head height (1.5 meters or so), you will need a 1200 gph pump to move 400 gph through 3/4 pipe.