Fat One Eyed Goldfish

Question
 Hello Nick and thank you so much in advance..
 I have a pond I built into my rear deck and it's about 350 gallons. I have two filters hooked up to it and the water quality is consistently good. I almost always feed my fish Crystal Clear Koi & Goldfish Food. One of my Goldfish, that I've had for years and has turned white, has been getting fatter and fatter. This started three years ago and I thought she(?) was pregnant but she didn't drop any eggs. The next year she added to her weight and this year she's gotten fatter still. I don't 'think' she has been pregnant at all any of those times. She also only has one eye but still does very well. She is swimming without any problems that I can see and comes running when she sees me headed for the pond at feeding time. She's so fat it looks like she has stretch marks on her sides.
 I have about 8 other goldfish in the pond, some have turned white, some are half white and half orange and the rest are orange.. I also have a Koi in the pond (Bubba) that is too big for it (abt.4lbs.) but it's the only place he knows and seems happy. When I bought him I was told he would 'only' get as big as his environment which he stated would be about ten to twelve inches when I drew him a picture of the pond and provided him all of the vitals.
I'm just wondering what this severe weight gain means? I don't want her to be sick as she's about ten yrs. old. All of the fish in my pond are 10 to 12 yrs. old and most of the goldfish started as 'feeder fish'. I'd also like to know why some change to white but that's just my curiosity.
I've only lost one fish in that pond. It was a Shubunkin<sp> and she/he was twelve years old and was a huge loss to us. We don't want to lose another right now.

Thanks Again Nick,

Bill


Answer
Sorry Bill, but this is a pond question. You will get a better answer in the pond section.

However, I do know that this is likely a disease called Swim Bladder. Caused mostly by poor water quality. In aquariums you add salt, increase water changes, and feed shelled peas to treat swim bladder. I do not know how to treat it in ponds, as I am not a pond expert.

-Nick