Carlos,
You can keep lines from stiffening by washing them with fresh water. An easy way to do this is to coil them, bind the coils with small line in three or four places around the coil and set the coils over the center spindle your washing machine. Then run a load as you would the laundry.
Be careful to bind the coils or you will have a drum full of the most amazing tangle you have ever seen!
Been there, done that.