To bind to the second value, use this code:
<span data-bind='text: csu_treatment_inputs()[1].value'></span>
Exemple: http://jsfiddle.net/v6T5T/
If you want to access an element from javascript, use this:
total+= parseFloat(self.test_values()[i].value());
Exemple: http://jsfiddle.net/v6T5T/2/