I chose to use multiple diffusers so that I could reduce the system down to just one in the shallows for winter time. This requires that you have multiple lines running into the pond, each being controlled by a valve. I also put a dump control valve at the pump to reduce (read "waste") the air so that I am not overpowering the one wintertime diffuser. Whether the vertex single diffuser can handle all the Gast 0523 can put out, I do not know, but I reduced the flow to be on the safe side. Actually, I do know that one diffuser can take a short run of full air flow, but I did not want to run it all winter that way...I did not need the massive boil to help control the ice.
As far as pure lift is concerned, the vertex published chart indicates that you get the same lift when comparing 2 x XL1's to 1 x XL2...
