Woah, that file is too big!

Hi --

So forgive me, but I'm having a little problem uploading a picture from Lightroom 3. Usually I don't have any problems, but this evening I decided to try something new, and did a focus stack of a bunch of images.

I exported them all into Photoshop as layers, did my thing, flattened then layers in photoshop, then saved.

The Tiff is brought back into Lightroom and and I try to upload it to SmugMug, only to find that its too big. Looking at the original tiff its 131MB.

Yikes, I'm shooting RAW with my Canon 5D Mark II and those files average about 23MB each.

So please enlighten me why my tiff is so huge, and how do I get an image like this down to a size I can upload and maintain the same high quality image.

Thanks!