return above or under

I'm in the process of doing putting my plumbing together and for my return i'm undecide, i've seen people do either their return above the water churning the water line and some plunging it under the waterline. My tank is rimless and without canopy so that in mind i was thinking a screen on top that i take off when i have guest. If so it would mean above water no? How's your set up and why? Plus is having your return churning the surface of the water a plus for gas exchange?

 

if im understanding this correctly, i would place mine just under the water surface pointing upwards (if thats an option) this is similar to my current set up, two of my power-heads point upwards rippling the water surface, ideal for gas exchange. make sure your sump can handle an unexpected siphon fro your DT should the power fail

 

Mine are above, or just below the waterline.. Helps with surface agitation

 

The outlet should always be below the water. If that's what you mean. Where it points is up to you. Up for more gas exchange or pointed to an area that needs more flow. You need a small hole somewhere as a siphon break. Put it just a hair below the normal pump running water line.
If you are asking about putting the outlet just above the water line the splashing will create noise and a lot of salt creep.

 

I voted "thru the back wall", but the correct level is about 1/2" or so below the waterline, aimed so you do get some surface agitation.

If you want supplemental flow, and you may be drilling the tank, look into adding a closed-loop. This will keep everything but the return fittings out of your tank for a much nicer look.

 

Below. You should get enough gas exchange with a skimmer running. I ran my return up through the overflow box out into the tank by having an extra hole drilled instead of over the back of the tank. If I was making the choice of over the back or through the back, I'd go for through the back on a rimless to preserve the clean look.

 

I currently run an over the back return line, which then goes back under the surface, with a small siphon break hole hear the surface.

On my 180 soon to be finished, I have a true coast to coast overflow along the top back wall. I'll be running 2 returns (split from one) over the back and then again just under the surface, with a small siphon break hole as well.

Lots of options- dozen ways to skin a cat.

 

Those are my thanks as of now, my 150 G starfire ;




and my 75 G starfire display refugium ;




The sump for both;




The return pipe for the fuge and its Herbie system ;