ML, I here you on the equations. I'm getting some help from a buddy of mine who is better at setting up and solving mutliple equations than I am. He's got some equations for me to look at but since there is the possibility of varying line sizes, varying distances, different diffusers, and different depths it looks like it will involve calibrating the system by checking the back pressure in each line by running all the air through the line and comparing that pressure against the published flow rate of your pump at that pressure. So you'll need your pump performance chart and will have to take several pressure readings prior to getting this done. In the end the equations will give you the pressure setting for each line that will result in equally split flow rate. If this turns out easy it may be a good alternative to expensive equipment. I'll be trying out on my pond as soon as I pick up two more gauges.
