04-05-2010, 06:44 AM
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If you have a sump than the water cascading down to the sump will oxygenate the water just fine. Adding an airstone will increase this, but is unneccassary, and will cause salt-creep, as others have mentioned. There is also a gas exchange at the water's surface, which is increased with agitation. I have my return pump outlets right at the water's surface to disrupt the surface. Partly for oxygenation, but more to keep the water moving and keep the buildup of that film of DOCs on the surface from forming.