Chris . . .
Thanks! Coming from a fabricator like you it means a lot.
Mike . . .
Our pond is 6K gallons. The foam is wet.
Airstone FF's are the simplest in terms of technology (check out the link I provided if you haven't already); they're also the least efficient. But they're dirt cheap and easy to build, have no moving parts, and cost nothing to run -- since they're 'powered' by an existing stone, etc.
I'm sure Erwin's unit runs rings around mine.
By the way, what brand did he get? What did it cost? And does it use electricity?