Pond Boss Forums AERATION Systems questions Figuring flow rate between pump & diffuser discs?

Im looking at a couple of kits/ pumps on ebay.

says 4CFM.

one states this

This auction INCLUDES:

*115 Volt AC, "Continuous Duty Rated Rebuilt Thomas Industries Pump: 400 Watt, 1/3hp with approx. 4cfm output. Draws just 3.5 - 4 amps (depending on exact depth of your pond). Rebuilt Thomas pumps do vary slightly in style, condition, appearance, etc. Output Specs will all be the same & They are all backed by a FULL 1 YEAR Warranty directly from us! We also service units we sell after the warranty period too, we can keep you up and running for many years at low cost!