Long Horned Cowfish "suffocated?"

[Philnashbass]

So, I purchased a nice 2.5" cowfish a few months back and qt'd it with a stars and stripes puffer for nearly three months. Great little fish with wonderful peaceful disposition. Planned to add it to my 120 gal. community reef when I was positive that parasites where of no concern.
Early this week I transferred it successfully to the 120 and it was swimming and healthy for the day.
The next morning I could not find it. I let it go for an hour or so, knowing it tends to slowly peer around corners and rock builds. I found it "stuck" to one of the powerheads. Not breathing anymore, I removed it from the tank before it could poison the tank. It had only been dead for a short time and the body showed no signs of trauma.

Perhaps I should have thought about the possibility of the powerhead problem, given the "weak" swimming characteristics of this species and will likely not get another for this reason. By the way, my qt utilizes a HOB filter and live rock only.

Two questions for you:

1. Is it possible that the "vacuum" at this proximity won't allow the fish to breathe and the death was due to "suffocation"?
2. Has anyone else successfully kept similar weak swimmers with powerheads?

[Hookup]

1. It is "possible" but I doubt it. 
2. I have kept pipefish in my reef (180g) with the Closed Loop running at about 10,000gph over 7 outputs and 4 inputs.

Reminds me to go looking for some dragon pipefish again actually...