It is very necessary to use filtration in a goldfish tank. They
actually require twice the normal amount of filtration (if you want
them to stay happy and healthy) I use two power (HOB) type filters and
at least one or two air stones on all my tanks. Whisper power filters
are fairly inexpensive and quiet. They can be used with or with out
carbon and you can find them at Walmart, Petsmart or any local fish
store.