[gilfish]

OK I'll start with any easy one. Most pics I've seen of the return hose from a canister filter have had it placed horizontally right near the surface. I was told it's good to have it there to ruffle the water and produce oxygen.

If I have 2 air sources already producing several bubbles on each side, can I position the return tube vertically and lower (not causing surface ruffle)?

Thanks!

[herefishy]

The reason the return tube is placed near the surface is indeed to "ruffle" the water. This "ruffling" does not produce oxygen, but creates ripples, or waves, which icrease the surface area and break water tension to better allow for the oxygen carbon dioxide exchange. Putting the return tube lower in the water column may have an adverse effect on the inhabitants and aquascaping of the aquarium. I've never seen it done, exactly, But it's your tank.