How do you change a crayfish tank?

You catch and remove the crays (If necessary remove all rocks branches etc first). Then you can syphon out the water and remove the gravel (Substrate). Clean and/or replace the substrate after the tank has been scrubbed clean. Then clean or replace all the rocks branches etc. Replace or clean (at most) 80% of the filter medium and refill the tank. Add water conditioner if necessary to remove chloramine/chlorine, adjust temperature and return the fish/crayfish to their home.