probably all down to temp, if you do move them into a bigger tank in your living room it might be a bit steadier otherwise stick a heater in it but turn it down to low 60`s, coldwater fish will live ok in more tropical temp tanks but their metabolism gets boosted
That's one thing you don't need with goldfish mate, they produce enough waste as it is. Room temperature is more than adequate for them to be healthy, water changing is more important in a tank and more so if the tank is on the small side. With that many goldies in a 2 ft tank I'd be doing at least twice weekly 40% changes with declo