Low fuel pressure

Having replaced both the in tank pump, the swirl pot and the main pressure pump and sorted out the bad earth on the in tank pump the fuel system now pressurises. However the pressure is low at 50 psi and the fuel looks like lemonade due to lots of air bubbles (cracked open a pipe at the metering head to view). There are no fuel leaks anywhere that I can detect so I’m puzzled as to where the air could be getting in. Car was running fine till the pressure pump died due to the in tank pump not running.car has had a new tank and filler neck about 6 months ago, so everything is spotlessly clean.

Check your connections at the swirl pot are correct, and that your pumps are both getting the proper voltage, as 50 psi is what the in-tank usually delivers.  You didn't mention the year so I can't be more specific, but if you are whipping air that is one thing the the connections between the in-tank to the swirl pot thru the other bits to the main pressure pump.  if you aren't getting @ 75 psi then you have some issues with fuel delivery,  When the pumps are pumping is there excessive noise?