Here we go again: MIs, Take III

[Samw]

Originally Posted by Aquattro

Just wondering how much photosynthesis plays in DO levels?

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

[Samw]

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

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[Aquattro]

Originally Posted by Samw

Photosynthesis adds oxygen.

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.

[Samw]

Originally Posted by Aquattro

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.

I didn't. I thought you were literally asking about photosynthesis which is specifically producing o2 as a result. So you really meant to ask what is the effect of cellular respiration (the opposite of photosynthesis). So as I said previously, in my tank when I had algae and no UV, my levels bottom at 50% (sometimes less) and now with no algae and UV, my levels bottom at 80%. I read in research papers that some reef fish like some gobies can survive in 3% saturation and damsels and cardinalfish around 10%-20% saturation. It goes without saying that different species will have different levels of tolerance to hypoxia. All of my mysterious deaths of established fish as I can recollect seems to occur when my skimmer was off overnight and always angels so far (pretty sure the MI would have perished too if it hadn't been relocated prior). Since the skimmer is in my DT, I turn it off when I do water changes, feed the fish, etc.

http://www.fondriest.com/environment...n-chlorophyll/

"Oxygen Depletion and Fish Kills
If an algal bloom appears, a fish kill can occur shortly thereafter due to the environmental stresses caused by the bloom. A fish kill, also known as a fish die-off is when a large concentration of fish die. The most common cause of this event is lack of oxygen 45."

[George]

I think (angel) fish dead overnight has some reasons other than oxygen. For a couple year, I ran a tank that has no skimmer. The tank had some very sensitive angelfish like golden and regal among other angelfish. All fish looked healthy and happy. As a matter of fact, one night I forgot to turn on my power heads after a maintenance. All fish were ok the next day morning.
I since upgraded that tank to a bigger one with a skimmer. But I am not hesitate to run a angelfish tank without a skimmer again. The only reason I wanted a skimmer in that tank was because I wanted to keep the water clean in order to keep some corals.

[Aquattro]

Honestly, even with O2 as a strong suspect, unless we monitor full time and chart values and find a sudden dip coinciding with a fish death, it's still mysterious dying fish syndrome.
The 2 in town that died. Tank is stable, nothing of any significance changes day to day, no power outages, etc. Fish survive fine for 6 nights, both die on 7th. What happened that could drop O2 to lethal levels on that night and not the others? Maybe something. Maybe not.

I did lose a MI and 2 large angels in a confirmed low flow setup overnight. I now have 2 MI doing well in a tank with surf conditions. But unless I spend a grand on an Apex DO meter and log O2 variances, we can't be sure what it or isn't happening.

[Samw]

In my case, it was reproducible. Flame angel a couple of times. Lemonpeel angel one time. Cherub another time. Always established for many months or years. Always after skimmer off overnight. Never a problem otherwise. If I had to guess, my DO level would have been around 20% (maybe much less. Eric's clownfish tank experiment had DO levels of 15%) without a skimmer running at night with a tank with algae.

Not saying this can be the only reason for mysterious death. But it is overlooked.

By the way, what was the reason for H2O2 dosing? To deal with an algae problem?

[Aquattro]

Originally Posted by Samw

By the way, what was the reason for H2O2 dosing? To deal with an algae problem?

Not sure exactly. General cleaning, I think. I confirmed with the tank caretaker that it's dosed a couple hours after lights come on, so no evening impact.