Meters can be rented from Hoskins Lab I think. A monitor that does 24/7 charting would be more useful than a meter because the data can be logged and one can go back to look at the levels from the logs when a fish dies unexpectedly at night. Those go for $2,000 though so not many people will own those.

Below is a chart of what I think is a typical a tank. The night bottom value might look low but that is probably typical for an aerated tank. I have no doubt that anyone running a skimmer in their system has enough DO. For those with tanks that are not aerated properly to begin with (using only powerheads or hang on back filters for example), the Idol could be fine for months but over time as algae grew or had a bloom, or the bioload increased, or there was lots of uneatened food one day causing decay and bacteria bloom, or summer came and the temp went up; then one night for whatever the reason, the DO drops just past the point needed for this particular fish and while it was fine for months, it unexpectedly dies (while everything else in the tank was ok). For tanks that have proper aeration (like a skimmer), DO wouldn't be an issue. The problem then is only turning it off and forgetting to turn it back on or turning off the return pump one night.

http://www.advancedaquarist.com/2006/10/review

http://www.advancedaquarist.com/2006...um/Figure3.JPG


If a tank has lots of algae, expect the range to be higher. Algae produces O2 during the day and consumes it at night. My results support this. When I had lots of algae, my DO range was large 50%-125%. When I had no algae, my DO range was small 80%-100%.

In this graph below (I think measurements from the Adriatic Sea), the spikes are due to algae growing near the sensor before they fixed it.

http://buoy.mbss.org/portal/index.ph...mid=58&lang=en

http://buoy.mbss.org/portal/images/s.../graf1_eng.png

The tank in question has constant flow and a large skimmer. Nothing changed between peak day and peak night, other than photosynthetic cycle. It is a very well stocked SPS tank, so I suspect that coral contribute to O2 consumption overnight

OK, I'll go with mysterious death, not DO related. :)

Just wondering how much photosynthesis plays in DO levels?

Forgot I was going to post a pic. Quick phone shot

http://i221.photobucket.com/albums/d...psjt9l6kgy.jpg

They look HUGE in there! Appear nice and fat in the pic though.

The pic does make them look bigger, but the big guy is a bit cramped. If he doesn't settle, he'll go to a bigger tank

Photosynthesis adds oxygen. With algae, I got plenty of supersaturation compared to having no algae. But my point was how algae can consume oxygen at night. In my system, it seemed to be significant. There are lots of articles on this topic.

Oh, the other chart didn't show up in my post. Here it shows what could be the oxygen levels of a typical reef tank throughout the day as measured by a $2,300 monitor from the other article. It varies wildly though depending on lots of factors. Some nights, the low will be lower and some days, the high will be higher. Shows the range from 3.5 mg/l to 8 mg/l

https://scontent-sea.xx.fbcdn.net/hp...ed&oe=559C23C1

Some things to consider for mysterious deaths :)

http://www.fishchannel.com/fish-heal...h-that-ph.aspx


Here is a case where someone was unable to keep flame angels after trying many including established ones. Looking at the list of equipment, I do not see an aerator like a skimmer. In my experience, I also had several healthy established angels (in separate incidents) die overnight when I turned off my skimmer (everything else was fine).

http://www.aquariumpros.ca/forums/sh...ad.php?t=30777

.

C'mon, you know what I mean. "Photosynthesis" as a cycle, so the respiration phase where organisms consume O2 :)

And who turns off skimmers, that's silly.