My grandson won a common goldfish about 3 yrs ago. Named him Goldberg. He's very active and seems to be very healthy still to this day. Shortly after we got him, we thought he should have a friend and got him a little white (goldfish) with an orange spot on his head out of the feeder tank at the pet store. It was a mix, it had a wider head and long tail fin, he named that one bomber. They got along well and then about 5 months ago bomber died. We went out after a couple weeks and got another one, because we feared goldberg would be lonely. Within 2 weeks the new fish died. We tried another one, same thing, within 2-3 weeks it died. We tried another one and this one lasted almost a month and it died. I watched them very closely because I have heard that one can bully the other, but he seemed to really like them. The new one's would follow Goldberg around, they hung out together, both ate well and they even slept side by side at night. He never showed any signs of aggression toward them. The newbies didnt show any signs of illness until 24 hrs before death. At that time they would get listless and hang out at the very top of the tank or the bottom for a day and then die. The last one we tried died 3 days after cleaning the tank, but with the others, that was not the case. Should we just keep him by himself?
I've never tested the water, we have a 5 gallon tank with filter and aeration and our original goldfish, goldberg is 3 inches long. The other fish were approximately 2 1/4 - 2 1/2 inches long. They've never had any red streaks on them other than getting listless approx 24 hrs before dying never exhibited any unusual behavior and were still eating. They looked just like the day we brought them home. None of the other fish were common goldfish, which I guess that is what he is. He doesn't have the fancy long tail, he's torpedo shaped and was won at the carnival. The first one that lived with him that I mentioned before (bomber) lived for over 2 yrs.
I've always done 10 percent changes once a week and then every 4 wks I take a gallon or so of the existing water out and put it in a glass bowl, then take the tank, rinse the plants, tank and decor and just wipe the tank out with a paper towel. Never using any type of soap or cleaner. I use the water conditioner for goldfish and feed them regular goldfish flakes once a day.
The other two fish that have died were goldfish, but one was a speckled (like a calico cat) although it was not one of the expensive ones it cost $2.00 and the other was bright orange and white with markings similar to a clown fish but again only cost $3.