Bloated photo size

I take a photo on my Nikon camera, open in Photoshop Elements, edit and Save for Web as a 800 KB jpeg. Later to save time I open it in Preview, crop & save and suddenly it's a 5.8 MB jpeg! So instead I open it in PSE crop and Save for Web as a 600KB jpeg. I sync it to my iPad and when I come to email from there it's suddenly 4.3 MB. What's going on? Can I get it a more sensible size on my iPad, and what's Preview playing at? Thanks.