You're going to have to raise the lid on that and place a fan on there to blow across the surface. A little more aeration with an airpump wouldn't hurt either.
Here's an article on keeping cool.
www.ReefReaders.com
And another about how to make a fan... I use these as permanently placed ones. But if you have the stuff, no other fan and are in a pinch....
www.ReefReaders.com
