Arnold + refraction = no alphas?

No.541874 ViewReplyOriginalReport
I'm trying to render an exploding bottle to compose it on a video, but no matter what I do I can't get the correct alphas in my output

Arnold just makes everything solid white (100% alpha)
The only thing that changes that is opacity, but it looks horrible when o turn down opacity, because it controls opacity of everything...

Is there a way to render the correct alphas with refraction without changing the opacity?
I don't want a black background on my render...

The Image doesn't have anything to do with what I'm doing, it's just to illustrate what I wanted to get, instead all the white part is solid white. With black background baked into it

Heeeelp