I lose 2 psi getting out of the cabinet because it starts with 1/4" NPT. I go out of the cabinet with 1" poly. It is over 300' to the pond, losing another 1 psi. I have a manifold in 3/4" PVC then 100' of 5/8" ID weighted tubing. I then go 3/4" pipe, split it still 3/4" then two 9" Vertex diffusers. I run a 4 cfm system down around 10' deep. My total system pressure is 8-8.5 psi. I don't think the diffusers are an issue at all.
