actually, the smaller the air bubbles coming out of the air stone the larger the over
all surface to volume ratio. which is why airstones can put so much more air into
water that just disturbing the surface.
now if those bubbles break the surface and rise into the air there is exchange both
on the inside and outside of that film of water.
an airstone in the water moves a water column up to the top and it flows outwards
creating a moving column of water that brings water from the bottom up to the top or
vertically. this is much better circulation than a venturi that moves water only
horizontally across the surface.
pumps should not be put on the bottom of ponds. too much chance of something going
wrong and the pond being drained.
Ingrid

Actually, the air water interface is at least as important, if not more
important. The larger the surface area of the air/water interface, the greater
the exchange of gases. While an airstone can pump air through the water, it
does so in a limited way, since it is only making contact with a small area of
water at a time and only influences the immediate area around the airstone. By
inducing a current across the surface of the water with a pump located at the
bottom of the pond, you will induce more gas exchange because of the greater
surface area involved. It also helps in preventing zonation from froming in the
water column, since you are pumping the water from the bottom and streaming it
across the surface, which in turn, allows oxygenated water to move towards the
bottom of the pond. The ripples going across the surface of the pond also looks
nice.




~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
List Manager: Puregold Goldfish List
http://puregold.aquaria.net/
www.drsolo.com
Solve the problem, dont waste energy finding who's to blame
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Unfortunately, I receive no money, gifts, discounts or other
compensation for all the damn work I do, nor for any of the
endorsements or recommendations I make.