Green Spotted Puffer Disease?

I purchased a Green spotted puffer about 2 years ago now, he was doing great along side a scat, and a couple killies. However recently he has been getting white splotches on sides, and tonight i noticed his side are sunken in and I fear i will lose him throughout the night. He was by far my favorite fish because of his great personality. I am sure I will replace him in time though he will always be remembered. I just feel like i need to know what this is in remembrancer of him and for future advice, I will post a link to his picture as soon as possible. Any help will be great.