YES!! Do you test your water? If so, I beat it shows you how crowded it is. You need at least 80 gallon for all of them and you need to start varying their diet by checking out the sticky Bel mentioned!
You are going to lose fish if you don't upgrade and I don't see how that is funny
They aren't feeder fish, that is not a type of fish, they are either comets or commons. The fact that they are feeders has nothing to do with the tank size. It's the fact that they are goldfish who are messy and need alot of room to swim around especially the slim lined type which you own!