That's because it is not eating. Give it time to adjust. I wouldn't even worry if it has been 2 weeks of not eating. Keep the tank lights above the tank off.
Once you reach the 2 week mark and it's still not eating, add epsom salt to the tank (1 tablespoon per 5 gallons for 3 days). Then proceed to saturate floating pellets or freeze dried food with an epsom salt solution (3/4 teaspoon epsom salt and 1/2cup of distilled water).