How long has it been up and running with fish?
Describe the lighting units (type bulbs, total wattage).
What are the current water parameters? Ammonia, nitirte, nitrate, pH, salinity, temp, calcium and alkalinity. Please post numbers of results.
As a precaution, do an immediate 25% water change
Also reduce your feeding to once every other day.
Signs of Ammonia Poisoning:
Fish gasp for breath at the water surface
Purple or red gills
Fish is lethargic
Loss of appetite
Fish lays at the bottom of the tank
Red streaking on the fins or body
ANY AMMONIA is DEADLY to fish. How high is your ammonia reading? Did anything else in the tank die recently?
How much live rock do you have (in pounds) and how long has it been in the tank?
Do you have any other filtration?