If you understood the nitrogen process you would have waited for your tank to completely cycle and not added fish until your amonia, nitrites are at 0. Then you should see nitrate. Did you tell the LFS your tank was just set up. Your fish is not depressed, it is in being poisoned, they can not tolerate amonia. If you still have amonia do not feed, it will just add to your bioload. Get that amonia to 0 then feed very sparingly. Your tank has to build up bacteria to be able to process the waste. Do a search for cycling a saltwater aquarium.