From the coupechouclub. There have been a number of versions of it.
As to the OP's problem, what is your sequence leading up to the coticule? I too would suggest not worrying about the HHT and using water only. My sequence usually is 1k > 3k > coticule with water. The coticule edge is always smooth for me, but I always need something more afterwards, paste, Thuri, or Welsh slate. Perhaps using briefly with water after 12k might help to calm any harshness. But I haven't tried this.