Bill you are right that any single disc diffuser that has any lifting capacity to it requires more than .7 cfm This is where the synergystic effect comes into play.(two discs on the same station) As Sue stated the Vertex dual disc model "CoActive Airstation" lifts a tremendous amount of water with 1 cfm per station (two discs)The rating for example at 12 ft depth and 1 cfm is 2778 GPM.If you take one disc away or seperate them you will not be lifting 50% of the dual disc capacity. This is where I feel single discs get very compromised as they require a lot of volume (cfm) to do the same task. However they are a great unit for the waste water industry where huge volume blowers are used and the discs are in very shallow water as this is what these single discs were originally designed for.They also have larger slits in them and produce larger bubbles.There are diffusers designed for ponds and lakes and diffusers designed for the waste water industry and it is common to see the waste water disc diffusers being sold for pond and lake use.How can you tell the difference?? Always ask for the "data" on the lifting rates at different depths and different cfm's and or the OTR numbers (Oxygen Transfer Rates) if they dont exsist or they are "top secret" and or require several cfm per unit (4-7)then you are probably looking at a waste water bladder type disc.Lots of good posts on this topic.