I run two Vortech MP-40's in the main tank. You'd think $800 worth of powerheads is worth something.
Is the tank super dirty? I didn't think it was, the fish ARE large, but it's a 180G tank with 5 clowns, two yellow tangs, one purple tang, one royal tang, two large damsels, a tiny wrasse and a candy hog. 13 fish in a 6 foot long 180.
The MP-40s are very strong, in fact if I move them higher up on the tank wall, they tend to create a vortech that sucks water in from the surface.
However, I guess the actual surface agitation was insufficient. I mean you can see the water is moving, but it's not "broken" if you understand what I'm saying. So maybe a gently moving surface just doesn't break the surface tension (or whatever) of the water/air interface enough.
A lot of aerobic bacteria? I have no idea how you could tell or not. But the tank runs a skimmer (in the sump, which was cut off of course) so typically it's not really dirty, though the fish DO eat and poop alot.
I'm convinced it's the surface tension/gas exchange thing. In tank flow will not help if the surface isn't broken. Putting the powerhead with air-venturi to dump bubbles into the tank had the half dead tang swimming again. Like opening a window in a sealed room with people in it.
I do have other pumps and will either add one that is less powerful, but does cause more surface agitation OR a HOB water-fall type filter to avoid this.
I don't know how long the pump was out, it was unfortunate that I came home 3 hours later than usual, it might have made a difference. But it seemed to be working int he morning, or at least I didn't detect that it was out (more reason for a high water sensor in the sump too).
The Jaebo return had been running for about two years I think. I'd have to check my never-updated wifebane tank journal.
V