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!

Be careful. I lost a gold flake, blue face and MI to this, presumably

Depending on how large the tank is, it could take a few hours. Lights off will increase the o2 consumption by the tank (algae, bacteria, etc).

20 minutes in and no noticeable difference in fish health.
-emperor is hanging below the feeder ring
-golden comes and goes through the rocks feeding on whatever it is as usual
-moorish is hanging out in th surf picking on anthias as usual.
I'll turn down the vortechs to 70%

Good idea...
Not really a control, but at least gives this topic a better sample size to draw a conclusion...

The funny thing is that if somebody with 10 posts, regardless of their actual experience, tried to say that a certain genus of fish was dying in their tank and the ONLY reason could be low oxygen, this board would be all over them telling them to test this, test that and double check everything...

That or condescend for buying a fish that is considered high risk and unlikely to survive in the first place.

If the MI isn't eating yet you need to bring out the fish crack... Pacifica Plankton. I kept a MI alive with it for 3.5yrs. Big, fat and healthy.

Speaking of oxygen demand I just got back from Hanauma Bay where I observed lots of MI pairs and Achilles pairs all in 4 to 8 feet of water and not a lot of current. Even got side swiped by about 300+ convict tangs as they raided the reef where an Achilles pair were living. Their territory was only about 4' by 6' and they were about 7" long. Think I need an Achilles in my 4' by 8' coral tanks. :-)

Tim, sorry, mine is eating well on a competitor's shrimps :) I may have some plankton in the freezer though, I'll try that tonight.

An hour in and I see no noticeable change in fish energy.
Threw some nori in for fun and it was the usual frenzy.
Total volume is over 500 gallons so I'll give it another couple hours. My sump turnover is around 8x per hour which could be a significant source of oxygenation but I would assume that with the skimmer off the DO would drop some...

One of the most frustrating things about this hobby is the number of variables from tank to tank.

I would imagine that your salt would also play a role in your tanks ability to store oxygen as would it's proximity to outside air...

This could be a pretty neat discovery if it turns out to have some merit.

Are lights off? if you have your lights on and have algae, you would be getting O2 from photosynthethis from the algaes in your tank.

Regardless of post count, I'm as experienced as the guy with 10 posts in this topic. I do have dead fish with no other explanation, but that's all I've got. I'm not will to try and replicate it to test :)

As for the morality of buying these fish, it's a topic for another thread, which I will bring up when I have more time to type.

Alternatively, lots of algae will contribute CO2 at night, which is when I lost my fish.

Yes, that's why for this test, one could turn off the lights to increase the depletion of O2 in the tank. See Eric's clownfish tank test where his DO dropped to 16% at night. And overflows are like waterfalls I guess so that is probably oxygenating the water. If that water is coming back into the display at large volumes, then the display tank is oxygenated no matter whether lights are on or off.

Even so...
it would seem you two are reporting extreme oxygen sensitivity.

Where do you draw the line for the threshold?

Now it sounds like the average set up with some algae, overflows and such would almost certainly be able to maintain appropriate oxygen levels.

No not extreme. Most other fish can tolerate these levels because it is not extreme. That's the point. Different fish have different tolerances to hypoxia.

I draw it closer than I would have last month. Otherwise "normal" setup, albeit pumps turned less than 30%, lots of algae, lots of dead (large) fish. MI first, then angels. Different evenings. Dog sitter would see fish at last visit, pick out a new body at 9am.

Right now, this is pretty thin guys.

Super interesting though and well worth exploring.

The fishes you have reported dying have extreme sensitivity.
not sure if you read that right (or I typed it right).

Yup. Agreed. However, I'm not willing to test this, just going to amp up the flow :)

How about we take this over here

http://www.canreef.com/vbulletin/sho...465#post936465

MI thread getting a bit off track.

Yup. that's what I said. The fish that are dying are extremely sensitive. But the conditions are not extreme. For example (i'm making these numbers up of course) most fish can survive under 50% DO saturation. Because most fish can survive at 50% saturation, this level is not considered extremely low. However MI and dwarf angels can not. So they are extremely sensitive. I made those numbers up to illustrate my point of course. I would have to measure the DO to know exactly at what point the MI starts to suffocate while all other fish do not. But it is probably at some level that most people do not think their tank is low on DO. DO fluctuates wildly depending on many factors. I've measured 40% before in my old system with airstone skimmer on with no deaths. My old system went as high as 130% during supersaturation by photosynthesis. With my current system, the lowest it'll get is 80% and the max is 98%. I'm sure that when I experienced the deaths overnight with aeration off, DO was well below 40%.

Sorry, you are right. The fish are extremely sensitive. I misread that the first time. The conditions do not need to be extreme.

Ok, no more O2 in this thread, I'm suffocating. hahha

So far, MI doesn't appear to be developing ich as I feared last night. Feeding some ich shield just in case.

So it's been over 3 hours without the skimmer running and circulating pumps at around 60%.
I can't say as I see any ill effects but I'm not going to carry it on through the night. Maybe someone else wants to try that...haha
Though far from conclusive I would say that I would be comfortable having run my system for a day or two without a skimmer. My fuge lights went on in the last 45 minutes so this adds another angle of discrepancy to the test.

Back to MI eating habits, does yours even go near that Ick shield? I tried feeding that to my display and not even my clown trigger would go near it!!!

Cool cool. Glad I was wrong on this. ! :thumb:

Ya, went right at it. I'm surprised, people told me fish often didn't like it.

Thursday update (it's Thursday, right?). MI and his Anthias buddies are all doing well, eating like pigs.
MI still has the same single whit spot, inclined to think not ich. Not sure, he won't stay still long enough to get a good look.

That's it. Simple update :)

What's this Ich shield we're talking about ?

NLS food laced with CP

Hmm
Guess we'll keep this info from the newbs :wink:
Don't need any overdoses happening here

Kinda late, there's a long thread about it.

Regardless of others opinions in the thread about ichshield , I've recently used it on two seperate systems and coincidence or not no more visible ich and it was bad both times around , I felt like what the hell before I tear down I'll try it out:)