Bob, Also note the Vertex diffusers pictured (as with most diffusers)have a range of operating cfm, too little and you cant keep them open or clean too much cfm can stretch them out and cause premature wear and the center check valve to malfunction and is a waste of power. In figure 1 depending on the size of the pump a lot of the air would go to the 100 ft run assuming a 3/4 hp vane @ 8.8 cfm and assuming the units were all at the same depth.Once the 100 ft diffuser maxed out (over stretched)air would be forced to the next in line would be the 200 ft run etc etc.Each diffuser in Fig 1 has a different friction loss to overcome since the supply tube gets longer, back to path of least resistance, If figure 1 was a 4.2 cfm pump you might open 3 or 4 discs.1 1/2 - 2 diffusers or you may have a small amount of air at each diffuser but not a lot of lifting capacity out of any of them.Figure 2 is the way to go but you still have to size the diffusers to the pump and vice versa.With the 4 unit set up as pictured a 3/4 hp(Gast 1023) 8.8 cfm vane will power those units a 1/4 hp (Gast 0523) 4.2 cfm will not.