I have not used Bootstrap but I worked on Zurb Foundation. On that I used to add space like this.
<div id="main" class="container" role="main">
<div class="row">
<div class="span5 offset1">
<h2>Welcome</h2>
<p>Hello and welcome to my website.</p>
</div>
<div class="span6">
Image Here (TODO)
</div>
</div>
Visit this link: http://getbootstrap.com/2.3.2/scaffolding.html and read the section: Offsetting columns.
I think I know what you are doing wrong. If you are applying padding to the span6
like this:
<div class="span6" style="padding-left:5px;">
<h2>Welcome</h2>
<p>Hello and welcome to my website.</p>
</div>
It is wrong. What you have to do is add padding to the elements inside:
<div class="span6">
<h2 style="padding-left:5px;">Welcome</h2>
<p style="padding-left:5px;">Hello and welcome to my website.</p>
</div>