Help optimizing code for combination of Numbers

I would like your expert advice on how to optimize the following code:

        private void PrintCombinations(int total)
        {
            for (int i = 0; i <= total; i++)
            {
                for (int j = 0; j <= total; j++)
                {
                    for (int k = 0; k <= total; k++)
                    {
                        if ((i + j + k) == total)
                           Debug.WriteLine(String.Format("{0},{1},{2}", i, j, k));break;
                   }
                }
            }
        }

For example, if we call the method as PrintCombinations(6), the results should be like:
0,0,6
0,1,5
0,2,4
...
6,0,0

The code above is non optimized. For example, code do not need to loop k form 0 to 6 to get 0,1,5 and 0,2,4.