kitch40

its done to aid in water movement more than for O2. As the water comes back down into the tank it moves it toward the bottom by gravity so there is a increased flow

Is it beneficial for 02 exchange? Yes. Although... if you have a skimmer without running biopellets it's likely a non issue. You want your powerhead to blow into an area of little resistance to get the most out of your powerhead. Consider trying to blow through a straw that you're holding your finger in front of, it slows down the flow. If you put your powerhead pointed right at a rock it'll slow down it's flow and reduce it's effectiveness. Point your powerhead into an area with nothing to impede it's flow. :-)

Heres another flow question? If you point your powerheads up to break the water surface, does that increase the amount that is evaporated? I used to have mine pointed up and it seemed to be increasing the evaporation. Now I have them pointed a little lower but they still move the waters surface. Good point about the skimmer, also if your using an overflow and sump/fuge, they pretty much do all the O2 exchange you need.

Here's another flow question? If you point your powerheads up to break the water surface, does that increase the amount that is evaporated? I used to have mine pointed up and it seemed to be increasing the evaporation. Now I have them pointed a little lower but they still move the waters surface. Good point about the skimmer, also if your using an overflow and sump/fuge, they pretty much do all the O2 exchange you need.