Image file sizes increasing on upload

I’m having a little odd problem where by when I upload an image I have optimized down to say 200kb, when its displayed on the site WordPress has actually increased the file size to 800kb.

My original 200kb file is shown in the media library but when using the full size version in a post it is the 800kb file that WordPress generated.

In the post the image has a file extension like this my-file-2592x1197.jpg which is the 800kb one. In the library it is just my-file.jpg which is the original 200kb file I uploaded of the same dimensions.

Ideas? I’m not sure if this is a WordPress or theme problem.

OK I seem to have found the answer to this. The theme I’m using has Aqua Resizer installed. Quality was set to 100% which for some reason made the resized versions bigger in file size. I’ve changed the quality setting to 80 and it has sorted it.