In my tank they are factor. Every morning that I forget to turn my aerators on after feeding from the night before, I find my angels gasping like crazy unable to swim properly and eat. On mornings that I leave aerators on, they are fine. Twice I left the aerators off too long and both times my Flames died. They definitely need aeration of some sort. It doesn't have to be skimmers. But powerheads are not enough. Do I need to turn off my aerators and take some video the next morning for proof?? Only my Angels (and MI when I had it) have this problem. Everything else is fine. Reading forums, I hear about Flame angels dying mysteriously all the time overnight. They don't die mysteriously. They die from lack of oxygen.
I could just put the Angel in my brother's tank and see how it goes. But I can almost guarantee it won't make it through the night although his other fish are perfectly fine.
I knew people would dispute this. I considered taking video last time but I didn't because it might be upsetting to watch. I wanted to show how angels gasped while other fish are fine in the morning. I could show that after I turn on my aeration, they recovered. Then I wouldn't sound too much like a broken record. If a fish gasps consistently in the morning under consistent set of conditions while other fish are fine, chances are the the differences between the 2 conditions (being the aerator being on and off) are what is causing that fish to gasp. In other words, some fish are going to need more o2 than others. If your angel hasn't died, that probably means, you have enough oxygen in your tank for that fish. It doesn't mean that this fish doesn't have higher o2 demands. In a heavily stocked tank, the most oxygen demanding fish WILL die first under low aerated conditions. This and the gasping is how I concluded that the Angels need more oxygen than the clowns, the gobies, and the wrasses, etc in my tank.
In my brother's tank, he only has a skimmer and a powerhead. No way, the Angel will survive if you shut off that skimmer at night.
Note that in my tank, the DO levels are 40% in the morning with my skimmer on. It is much less with it off. In the Reefkeeping article, the clownfish tank had about 16% DO saturation at night without an aerating device (but had 2 powerheads used at the surface). With the skimmer running, it was 90%.
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