It depends on the depth of your pond. livingwateraeration.com does a great job of summarizing it. "The deeper an air diffuser is located, the more boiling action it will create and a larger area will be aerated. Therefore the deeper your pond the less CFM needed to aerate your pond. 1.5 CFM of air can effectively aerate a 1 Acre pond at a depth of 12' or deeper. The chart below can be used to determine the size of the compressor that you will need, it is based on a compressor producing 1.5 CFM of air." - See more at: http://www.livingwateraeration.com/poaeinpa.html#sthash.o0Mjq0Q2.dpuf
