What's the deal with the black crays? They need a crazy PH or something? I was looking into them as well a week ago and found that they are really hard to keep. It's too bad, they are gorgeous looking.
They have very specific pH, temperature and dietary requirements. They seem to kick it at the slightest error in the water, so you have keep pristine conditions for them. Personally, I haven't tried to keep them yet just because I haven't seen anyone keep them long enough to make it seem like a worthy investment in money. All the serious cray keepers I know, at best they got a month or so out of them before they kicked it. Gorgeous, though, one day I'm going to get them.
Prawns are seriously awesome. I want to get more, but I don't have the space for another tank...
those black cherax with red antannae are cherax preissii. they are a little hard to keep. i also would not order from that website, liveaquaria, they sold me the wrong thing and it took almost a month to get any kind of resolution. their customer service is nonexistant and the guy in charge is NEVER there. just a girl named nicole who answers the phone then will "contact the owner", which means do nothing until you call again in a week.