likely poor water quality. how many goldfish do you have and how large is the tank??
start doing some water changes- remove 25% of the water and replace it with water that is ONLY dechlorinated every other day for a few weeks and get some antibacterial FOOD and feed it to all of the fish. also get a bubble stone with an air pump to circulate the water around.
Chris- Husband, 04/30/77
Cailyn- Daughter, 07/05/99
Jeffrey- Son, 03/24/06
Alex- Son, 03/25/09
Mister- Black LabX, M, 08/06(?)
The Shadow Stalker- Gray Tux DSH, M, 04/04
The Mighty Hunter- Black Tux DSH, M, 04/04
Baby Girl- Tabby DMH, F, 12/03(?)
Frances- Tortie, DSH, F, 2007(?)