Through their anus, same as you.
Goldfish excrete, yes.
Yes
48kg per hour
About 3 and a half kilograms
Under normal circumstances, it is best not to mix goldfish with other fish. They excrete higher amounts of ammonia, and it is harsh on the other fish in the tank.
Tetras (unlike goldfish), do not excrete a lot, so in essence they would be "clean" fish.
There will be a problem either with the water or the diet. My advice is to do a few large water changes taking all the proper precautions and equalising all parameters. Then I would improve the fishes diet by adding a feed of earthworms at least once a week.
no, clouds not excrete
Some common breeds of goldfish are: the Black Moor goldfish, the Ryunkin goldfish, the comet goldfish, the common goldfish, the Calico Fantail goldfish, the telescope eye goldfish, the bubble eye goldfish, the pearl scale goldfish and the Oranda goldfish.
yes plants do infact excrete
Ferrets excrete to get rid of waste
All living things excrete.