Culligan mark 100 water softner water flowing to brine line all the time

is this normal if not what could be causing it

Yes it's normal when there is a problem with the control valve being stuck in part of a regeneration instead of going back to the service position after regeneration.

Usually the problem requires a new piston, seal and spacer kit or motor etc.. You usually can't get them to tell you what is wrong or sell you the parts to repair them yourself but... call the local dealer and see what they say.