Goldfish Redprints

Question
Until recently, my green goldfish has been living alone, and had a faint red spot on top of his head ( he is about 9 years old ).  About one week ago, I got two new smaller goldfish who seem to be fine with the tank.  The second day the new fish were in the tank with the old one ( I got a new tank with my new fish ), the red spot got darker and spread down his back.  Is there any disease that he could have and is it contagious?  I appreciate your answer to my question.

Answer
Hello Zach,
Are the spots on the fish dark reddish or are they like a lightish red? It could be ammonia burns or an infection so I suggest you to use the API Stress Coat+ or the Stress Zyme+ which you can buy @ your local petshop such as Petsmart or Petco for about $9-$12. The average goldfish life span is 15-20 years so I don't think it's because of the age. Separate the green goldfish in another tank so the disease won't spread. Change 25% of the water everyday and make sure that the quarantine tank has a filter too.
Hope this helps!
~Sam