Kurt wrote:

Better than airstones are to add a venturi to the pump.

It depends upon whether you have a water pump already. A venturi is
pipe with a hole in it. When the pipe has water flow through it, it
creates a vacuum in the hole due to the venturi principle.

With a water pump you flow the water through the venturi and suck air
into it. Its work on the same principle as the aerator on the faucet in
the kitchen sink or bathroom sink.

If you don't need to pump water then a water pump is unnecessary. In an
air stone you are pumping air, not water. Air is very cheap to pump.
Air is what you want in the water. You don't need a venturi. What is
better than an air-stone is a aeration diffuser head.

If you do need to pump water, then a water fall or fountain or venturi
are alternatives to an air pump and air-stone or aeration diffuser head.
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18,000 gallon (17'x 47'x 2-4') lily pond garden in Zone 6
Cheers, Steve Henning in Reading, PA USA