BV, if I had the *slightest* idea of how to explain barometric pressure, I
would. Unfortunately, I can't. But maybe someone else can . . . How it works
is something else: as the bubbles rise, they displace the water. New water
moves in to replace the air bubbles, and pulls the "stuff" with it, drawing
it more towards the drain. The oxygen benefits of the air diffuser is pretty
much self explanatory. Folks that had regular covered bottom drains and
upgraded to the "air domes" swear by them.

Lee

"BenignVanilla" wrote in message
...

"Lee Brouillet" wrote in message
...
Now, if you put an air dome on it, you
literally change the barometric pressure on the bottom; the rising air
bubbles assist in pulling the crud to the drain. And the air bubbles add
extra oxygen to the water and give the koi additional play areas.

I am still baffled by the air bubble thing. Can you explain further?

BV.