The instructions online said 1/4 teaspoon per 40g, so I took a half shot glass of vodka I found in my pantry (impressed I had any at all, I'm not sure where it came from !!) mixed 3/4 teaspoons powder into that (tank is a 115g so I rounded up to 120g), it turned a bright pink, I stirred it for about 2 minutes. It was definitely not very soluble still, lots of particulate in the tank that took about a half hour to settle out. Did notice a nudibranch looking thing I'd never seen before floating around (maybe it was a big flatworm? I dunno) so I think some effect must be there.
I did call around and did find a LFS with Prazipro, just basically ran out of time today and couldn't get to that store but I'll be able to stop by tomorrow. I can see the advantage to a bottled solution over something I have to mix myself.
So I should be ok to hit the tank again tomorrow? Man, I absolutely hate the idea that I'm nuking my display tank but I don't see what other option I have (at least there are plenty of stories out there to reassure me that the tank ought to come out the other side!)
I'll see if I can post a picture of the tang. His face is covered in ulcers, there are ulcers along his back and one of his fins is a bit eroded as well.
I just hope made the right call deciding that it's flukes and it's not something else.