The surface of my tank would probably be classified as violent :) I pump from the bottom up with a couple of the pumps, it can't get much more violent and keep the water in the tank. Much more flow than I had in the 90g with all the fish before going into the DT. I think the heavy cyano and hair algae had a part in the low levels at night as well.

Well, that's the thing, you have lots of flow. But flow doesn't oxygenate water. :) Right now, we're guessing. Once you have the readings, then we won't be guessing. Yes, algae, cyano, bacteria and tons of stuff will consume the o2 at night. But as the article showed, an airstone or skimmer, took care of it.

Breaking the surface is what forces CO2 out of solution, not adding air bubbles. All an airstone does is force water from the bottom to the top, breaking the surface, so a pump doing the same is the same.
I also have a skimmer going, which is a big contributor to off gassing CO2.

An airstone isn't going to happen, too much salt creep and bubbles :)

Yes I realize that, but you'll need a small water fountain to get the same results as the air stone or protein skimmer. Even hang on back filters which breaks the surface does very little compared to the surface breaking of an airstone. But OK. Maybe you have a lot more splashing at the surface than I thought (which would also result in salt creep).

I can hear it in the next room :) No salt creep, it's centered in the tank.

This is the newer model of the one that I use. $349 USD only. Excellent condition.

http://www.ebay.com/itm/Oakton-DO-11...item5670b2ccf5

Why not incorporate more waterfalls in the sump between the different chambers? A few more pieces of glass at different heights.

The problem isn't in the sump. The skimmer is already efficiently oxygenating there. It is when the return pump is set low and the water being returned to the display tank is reduced that is the concern.

Mr MI may be developing Ich, not sure yet. I guess I'll know tomorrow night, at which point I'll treat the tank with CP.
Still not eating nori, which would help relieve stress, I think.

Interesting thread on oxygenation....
I suppose I should comment on my MI and his feeding habits to keep the thread on track before I get into the oxygenation.
At first my MI was all over mysis and then slowly switched him to seaweed extreme pellets. Once he was eating well I slowly weened him off the seaweed and got him on 2mm nls. Since then I feed a mix of seaweed extreme, nls, and nori which has recently become his fav. He lives with an Achilles who is an ich machine but seems to be healthy enough not to share the outbreak. Had him over 6 months and he is growing so I'm optimistic on his success.
So back to oxygenation.... I'm going to turn my skimmer off to see how my emperor, golden, and MI fair with lower oxygenation.
I'll keep you guys posted!