What accounts for the difference in the slope of the plots of the conductivity of three 1.0M solutions?

We did this lab where we took distilled water and added 0-8 drops of an electrolyte to it and then tested the conductivity of each after each drop and graphed it. So why is the slope of Aluminum Chloride greater than Sodium Chloride and Calcium Chloride? Each original concentration of the solutions was 1.0M.