As I planned on using 2" net pots for growing the lettuce, I decided to use 3" PVC tubing for the main tracks.  This size of tubing, combined with the dimensions of the frame, allow for and even 5x5 grid for the net pots.  The net pots are evenly spaced from each other at 6" in both the x and y directions, allowing for easier setup with our program later.  I used 1" PVC for the end where the water flows into the system with ball valves to allow for flow control.

    The main difference with the plumbing in my current system is that the tracks are not all connected together.  In most system of this size, the tubes would be positioned in a way that water flowed into the system from one track and traveled through all of them before being deposited by the last track.  There are a couple of reasons that I chose to feed each track individually, primarily for the gantry and flow control.  The current layout allows me to put all the tracks at the same heights, making it easier for our gantry to interact with each position.  In addition, I put valves on each track to control their flows individually.  The reason I want to control the flows individually is because the track closest to the water inlet will always be stronger than the one farthest.  Also, if someone wants to stagger the grow period of each track (to have some lettuce each week as opposed to a lot of lettuce all at once, for example), they can cut the flow to the tracks currently not in use.