Thanks.It will benefit your bio media by providing oxygen rich water, the oxygenation process mainly occurs when the bubbles break surface tension and exchange gas with the atmosphere - so the air stone would have the same benefit no matter where you placed it in the tank or sump. It wouldn't hurt to have extra water circulation in your biomedia if thats something you want to do.
Water can only hold so much oxygen. Once its saturated with oxygen thats it. most tanks are adequately oxygenated from filters and overflows. But having extra definitely does not hurt aside from the added potential of evaporation from all the bubbles.
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