It has all been said.  The ...

It has all been said.  The issues are water or tank with a chlorine demand.  Circulation of the water once full taking water from the bottom and pumping it to the top of the opposite side.  Dosing the hypochlorite once there is a thin layer of water and allowing mixing as the tank fills.  This can also fail if the water filling is too gentle because the chlorine can still layer.  Mr Patel's is good advice.  I have too many clothes with holes in because of splashes of hypochlorite so certainly wear PPE.