Check for max value of iterative sum in pandas

I believe you need a cumulative sum and then to locate the max.

>>> df = pd.DataFrame({'a':[-0.000601, 0.000001, 0.000000, 0.000007, 0.000300, -0.000300]})
>>> df

out:
          a
0 -0.000601
1  0.000001
2  0.000000
3  0.000007
4  0.000300
5 -0.000300

>>> df['b'] = df.cumsum()
>>> df

out:
          a         b
0 -0.000601 -0.000601
1  0.000001 -0.000600
2  0.000000 -0.000600
3  0.000007 -0.000593
4  0.000300 -0.000293
5 -0.000300 -0.000593

>>> df[df['b'] == df['b'].max()]

out:
        a         b
4  0.0003 -0.000293