I suggest you read through all the helpful threads in New to saltwater forum. There is so much to learn about this hobby. The learning curve is very steep.
New systems have lots of stability issues. Pictures would be helpful in assessing what is going on with your fish. Tank parameters would also be helpful.
What is your sp. gravity? temp? PH? what are your tank inhabitants? Is there aggression between your fish? Are you keeping any corals in the tank or just fish?