Don't let your guard down, it took my blue crayfish almost two months to decide to eat my goldfish. But once he decided..... boy did he do a good job. So keep an eye out for agressive behavior, dont overlook missing and torn up fins.
Crays usually go hunting at night... hope your angels don't decide to sleep near the bottom of the tank. make sure there's food right before you turn out the lights.
dead fish that aren't diseased(!) that sink(!!) work great or mussels if you have them; basically the stinkier the better - hikari canivore pellets are always good imho, although your angels might be tempted too... which sorta defeats the purpose heh
my blue cray is rather slow...
I do find nipped or clipped fins from time to time, but have yet to see anything really bad or find a causulity.. kinda fun sometimes watching him try to catch them....
i had a 5" one and its color could have got it first place in a fish show. It was a pure shape of a purple-blue pix, a little off from royal blue. I have a shirt that he just blended right into I will have to get some picks up! its dead now