Unlike most aquarium fishes, Marbled Crayfish are not picky about water.
In our experience, most of the water in the USA is hard water, more so in the southern states.
Marbled Crays seem to like the temperature “cooler than tropical” meaning 72-76 degrees seems to suit them better than 78-80 degrees of a tropical fishtank. Our personal experiments show us that they can live through extreme temps in both hot and cold – even though they will not reproduce in extreme temperatures.
But otherwise, they are not picky about PH, they do just fine in water straight from the tap. “Conditioning water” for days like is done in a tropical fishtank, is a complete waste of time.