Likely ammonia poisoning which will stress the fish and allow disease to take hold. Until the tank is cycled, you should be doing daily water changes of at least 50%. Goldfish produce A LOT of waste for their size.
Do you have a test kit to see what your water parameters are? Most local fish stores will do a free or inexpensive test if you ask. You should be monitoring ammonia, nitrite and nitrate.
PRIME as a water conditioner can detoxify ammonia and nitrite (read the label carefully for treatment of high nitrites). It does not interfer with the nitrogen cycle. |