I thought my tank had lots of O2, but I had turned the pumps down, thinking the lower setting plus return pump plus skimmer would do the job, and lost my 3 larger fish. MI first, then the 2 angels. Low O2 is the only answer I have..

Makes sense Brad. Your sump with the protein skimmer was highly oxygenated but that oxygenated water was not coming back into your main tank fast enough because of the reduced return flow. Night time deaths of the highest O2 demanding fish would result when DO levels drop at night. For most the easier to keep and less demanding fish, this would not be a problem.

If I turned off my skimmer tonight and only leave my powerheads and an aquaclear running, tomorrow I will wake up with dead dwarf angels but no problems with everything else in my tank including tangs. Happened every time.

Brad, mine wasn't eating anything for a few days until I started putting some garlic extract in the pe mysis, it had a couple of nibbles and after a few feeds it definitely perked up his appetite. Now I am not sure if it had internal parasites or not but the garlic extract acted as immune system and appetite booster. It is now also eating large amounts of purple nori.

Sam, correct. Skimmer is good, but flow back to tank is pretty low. I'm going to rig a small Tunze to agitate the surface at night when pumps are lower

Interesting point on the dissolved oxygen level. I will have to keep that in mind.

Yeah, that's my biggest fear too. I recently bought and installed a Penn-Plax battery-operated backup air pump so I don't lose fish during power blackouts. Sorry to hear about your MI....

I only lost fish, could have been a lot worse!!

smaller mysis? my fish won't eat the heads....:rolleyes:

Anyone have any research on this or is the current theory based solely on 2 board members shared conversation and experience?

Seems like if proven and not common knowledge, should be a pretty important piece of information for the hobby.

I think this is all we have. I haven't read anything else about it anywhere. Assuming enough O2 is present, are they still super difficult? Probably..

My DT has flow enough for surfing across the surface, so we'll see where I end up in this trial.