My Goldfish has missing scales; what do you think it is? (Pictures Included)?

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Please help I have had my goldfish for 10 years. Recently I got 2 goldfish from a petstore but they died I'm afraid they could have given my Goldfish some sort of infection?
Update: I have 4 Goldfish that I won at the carnival 10 years ago. Well they have a pretty big tank and a great filter we change it all the time and the routine has been normal for 10 years, so I wouldn't think that is a problem. The only change was when I got the 2 small goldfish at Petsmart they started loosing their... show more I have 4 Goldfish that I won at the carnival 10 years ago. Well they have a pretty big tank and a great filter we change it all the time and the routine has been normal for 10 years, so I wouldn't think that is a problem. The only change was when I got the 2 small goldfish at Petsmart they started loosing their scales and I'm afraid that those fish could have had a disease?
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