Saltwater lethargic fish

Question
Saltwater 35 gallon tank. 3 months old. Water tested with high nitrates and advised to change 10 gallons. did that. the fish are lethargic. sitting on bottom or a few hang at top. no swimming around. Bullet Goby not sifting sand for two days. have live rock no coral. What's wrong :(

Answer
Anything could be wrong, you could have mixed the saltwater wrong, you could have introduced something toxic to the tank somehow, the water quality could be getting bad. any of these could lead to lethargic fish along with many other possibilities such as parasites or infection.

hope that helps

Marcus