stingray floating on top of water?!

[JeremyXXXX]

I never thought about the sump tank, it creates oxygen in it's own by the fall of the water.

 

[DavidW]

Oxygen exchange takes place at the interface/surface between the air and the water. This is why your rays swim at the top of the tank when the water is oxygen depleted.
Bubbles create HUGE surface area in addition to the top water surface of the tank, and also agitate the water, so they oxygenate the water better than any power head, which just moves water around but doesn't increase air/water surface area.

 

[Just Toby]

I hear that agitating the water with powerheads does not create the oxygen and then I hear it does. I believe it does because the night that I almost lost my rays all I had was my powerheads, I pointed them upwards and they started to breath better.

I have airstones now and I notice no real difference if i use just powerheads or airstones.

Airstones add water by agitation of the surface...my earlier point is that some people think the bubbles are adsorbed by the water...it is the surface agitation that does it. If the power head ripples the surface then they do the same job to a lesser or greater degree depending on the amount of surface agitation.

I have a koralia circulation pump as used in marine tanks and it ripples the water to a massive degree, as much as any airstone could.

If you are really concerned then measure it using a redox probe...it is probably the only way of knowing how much orp (oxygen reduced potential) is there. But as long as the surface is rippling then you are fine.

You made a point about the sump adding oxygen but that is not totally reliable as the massive bacteria present in the sump will deplete the oxygen before it returns to the tank.

I have 4 eyeballs pointing at the surface so the water coming back from the sump ripples the whole surface thus adding the oxygen back in.

 

[SpeshulEd]

I have two koralia 8's in my 450...my surface agitation is about as good as it gets without giving my fish whiplash, haha.

 

[JeremyXXXX]

I wish I had a sump I always find myself skimming the surface of the water with a net for stuff.