the toffee must reach the correct temperature or it will not be brittle and hard when it sets. It is worth investing in a sugar thermometer. That said, the toffee still tastes good even when a little soft and sticky but it won't be real Toffee. The success of this toffee depends on it reaching the correct temperature, any lower and the sugar doesn't melt sufficiently to produce a sharp, hard toffee. Adding water, not butter, creates a very brittle, shiny toffee, butter would make it cloudy.