I bought a venturi from this website: http://www.mazzei.net/agriculture/index.html
I was considering to make a fountain or splash my well water over rocks for aeration, but I did not want to have freezing problems in winter. My water source cycles off & on frequently since it comes from the discharge of my geothermal/ ground source heat pump, so the discharge pipe can freeze up if exposed. I think this inexpensive venturi was a good solution for me. I keep it about 5 foot deep so I get some mixing and water circulation. The bubbles are not extremely small but I get 0.5 scfm of free air for the 5 gpm water discharge.

Jeff Gaines