I have kept a blue knight crayfish before. These guys are quite cool to keep. They don't need a lot to keep them happy. First thing you need is a few caves. These guys like to back into thier caves as if to say they are hunting. Next you will need lots of things for these guys to climb up on. Third thing you need to keep in mind is put all of these items basically in the center of the tank. This is for a few reasons. The main reason being that they generally like to run around the "outside" of the tank perimiter.
Be fully aware that crayfish are EXCEPTIONAL escape artists. If there is a way that they can get out of your tank, they will. This means ANY cords or filters on the back of the tank should have the smalles openings possible. Infact, it is a good idea that if you use a HOB
filter to raise the back flap of the plastic so that it can cover the exit for the filtered water and this will deny the crayfish an easy escape.
When i kept mine, i kept it with a fluval 2 internal filter. That ment i had 2 small triangular cuts in that plastic top backing, one for the heater and one for the filter. It is a VERY good idea to go with a heater that can have a protective case put around it (much like Tronic) as your crayfish may be like mine and like to sleep on the heater itself.
Do not put any sponge in this tank as your crayfish WILL shred it and make a mess of it. I have learned that from experience. If you minimize the holes in the back top of your tank, i personally believe that is the best. Your crayfish WILL climb your cords quite often and mine would actually hook its legs around the plastic edging many times and walk around the top perimiter of te tank that way looking for new adventures.
When it comes to food, it is best to serve these guys shimp sticks and spirulina sticks. Alternate the days so that it is shrimp one day and then spirulina the other. Remember that what you feed him/her will affect thier coloration in the long run so if you vary your food, it will keep them more natural in coloration.
If you want some alternative lighting solutions you coul try LED
lights. I actually used the new Marina LED
lights that can come solo or you can buy a 3 port hub and 3 adaptable lights. Since you can't add plants (again because they will be eaten and ripped out or clipped off) LED
lights will do fine. You can actually have it so your tank is blue, red or green. Because crayfish are nocturnal, these subdued lights will actually make him much more active throughout the day.
Hope that information helps