Mainly ammonia from there pee. No matter how good your filter is or how clean you keep the tank you still need to change the water. Also artificial decorations collect a bacteria that is harmfull to the fish need to keep them clean also.
It is probably sick
Obviously they can get sick just like any other creature.
they might get the "ICK" or they can get sick from there bowl or tank not being clean
MythBusters - 2003 Sinking Titanic Goldfish Memory Trombone Explosion 1-15 was released on: USA: 22 February 2004
because they are sick dummy
Sometimes maybe when its sick or something.
If your goldfish eat a lot it means it is lazy.if it eat a little that means it is sick
Depending on what your sick goldfish has, it will either be specific to that fish, which you should place in a separate tank to treat, or it's something that will spread to other fish in your tank, in which case you will need to treat them all.
who knows. maybe it's sick.
No. Goldfish in fact are basically the fish that will get sick the SLOWEST because they are extremely hardy and have almost no requirements other than food and water.
when your goldfish gets sick you can either take it to a person who nose how to handle with fish or you can just leave it and let it dye because i"m just saying that it is part of there life.
Usually when they are about 2-3 years old. Goldfish can also die if you don't feed them enough, or too much. When goldfish are not kept in a clean habitat, they can get sick and die. Make sure to clean your goldfish tank at least once a week. Remember, goldfish mainly die from aging