gzip with codeigniter

In your config file change compress_output to TRUE. I think it uses gzip.

There's also this disclaimer:

VERY IMPORTANT: If you are getting a blank page when compression is enabled it means you are prematurely outputting something to your browser. It could even be a line of whitespace at the end of one of your scripts. For compression to work, nothing can be sent before the output buffer is called by the output class. Do not "echo" any values with compression enabled.