I was testing my website with Page Speed and the result was around 70/100. Enable Compression was the first and most important factor in slowing it down.
I know that
I'd suggest to use http://php.net/manual/de/function.ob-gzhandler.php, this works out of the box for me:
In my index.php I just place this before some output:
/** * Enable GZIP-Compression for Browser that support it. */ ob_start("ob_gzhandler");
And it encodes it!