Goldfish with Digestive Disorder

Question
Hello:
My son's goldfish is almost 9yrs old.  He's a plain comet "PRIZE FISH" that he won at a school fair in Kindergarten.  He's kept in a 10gal tank with Whisper filtration system.  He now has a 6" long body with a 2" long tail.  Lately he hasn't been unable to produce good POOPIES.  He seems unable to produce the casing.  What can we do to help him?  I have been changing the filter every 2wks and change the water by 25% monthly.

Also, he has an eye infection and seems to be blind in one eye.  I treated him with Melafix and Jungle's Fungus cure, but it keeps reoccuring.  He really wants to swim and RAMS into the glass and injured his mouth and face.  I might be able to place him into a 20gal tank as soon as I clear a countertop space.

Your immediate reply is appreciated.
Thank you,
Geoffrey's Mom

Answer
Hi 'Geoffrey's Mom';

Wow! Nine years! You guys have really cared for him well. Their normal lifespan is well over ten years but most die far too young. He's lucky to have you for a friend.  

He does need more room.  A ten gallon is a minimum size for goldfish as adults. His frustration in not being able to swim will continue to cause injury as he tries. He also needs more frequent water changes. All tanks need a 25% change every week. Especially goldfish because they are so messy. Vacuum the gravel too. It's hard for him to heal and get over the eye infection if the water has too high a level of nitrates. Nitrate (NO3) is the end result of the biological filtration that occurs in your tank. It can only be removed by frequent water changes. You can have the water tested at your local fish store, or just get your own kits to check it at home. If you have it tested at the fish store, have them write down the actual results. It is very common for them to say "it's fine". "Fine" means very little in regard to water chemistry. Especially if the fish store employee is not very experienced. What components did they test for? What were the actual levels? It's really important to know the details. Nitrate (NO3) should be less than 40 ppm, ammonia and nitrite (NO2) should be "zero". PH is okay anywhere from 6.5 to 7.8.

When you say "casing" about his bowels, I'm not sure what you mean. I will assume it's about the firmness of it. When fish poop, it should break off and dissolve into the water before it reaches an inch long. If not, he isn't getting enough fiber in his diet. He needs vegies! A few times a week he needs cooked and peeled peas, raw romaine lettuce, cooked shredded carrots, slightly cooked squash chunks, raw cucumber slices, or cooked green beans. He can nibble on them all day long and helps with boredom too.

Followups welcome....

At Your Service;
Chris Robbins