Well, it looks like I'm going to have to make some major modifications. I expected as much, so it's no big deal.

First, I am going to remove the clear PVC down tubes. They sound good in theory, but I find that the foam flows too fast through them to make accurate adjustments. Also, what I happening is that the foam exiting the injectors is under so little pressure that when it hits the water in the skimmer body the bubbles collapse into each other. Coincidentally, bubble size varies too much. I also think it is responsible for a lot of the turbulence in the skimmer.

Second, I am going to move the recirc pump. I had it positioned at the front of the skimmer, under the window. Doing this forced me to use a long piece of 1 1/2" spa flex and multiple ells to get the outlet directed to the back of the skimmer where I had room to connect the injector plumbing. By moving the pump to the back of the skimmer, I can reduce the amount of piping to the injectors by about 80%. This will increase pressure to the injectors. Right now, if you were to turn one of the ball valves before the injectors even slightly, the injector would all but shut off. This tells me there is far too much head loss.

Third, I am going to replace all of the Beckett housings with machined housings using PVC plate and clear PVC tubing. The housings I am using work and are cheap, but I am limited to a 1/4" NPT ball valve and that is proving to be inadequate. I plan on using 1/2" needle valves. This will allow for much greater air flow control and allow me to plumb the air inlets with 1/2" PVC and to direct them above the skimmer to prevent water from shooting out when the recirc pump shuts off. The 2' of 1/4" tubing currently in the valves restricts the air flow soo much that the valves must remain full open. This prevents any adjustments.

Overall though, I think this will be a great skimmer.