Auto feeders are arguably useful, Run a search for them in the DIY forum and you'll get several good discussions and experiences.
It seems that ammonia is what she was testing for. Ammonia causes gill irritation and will result in permanent damage if the fish is exposed to for any length of time. Water changes are the best way to reduce it, and cutting back on feeding will help your cause immensly.Fish can and will go for a week or two without food added and suffer no negative effects. One danio doesn't need much food. I would feed once every 2 days an amount equivalent to the size of his eye (no I'm not kidding and this isn't cruelty) He will be fine and you won't have excess food creating extra ammonia.
Don't be at all suprised that the girl at the LFS doesn't know what she is even testing for. She probably heard that ammonia causes stress, and she is gauging stress on your fish based on the ammonia test level. If it showed yellow at all it's too high.
If you don't have your own test kit for ammonia, I would start with a 50% water change and then do a 25% daily until you get through the cycle.
And read up on the nitrogen cycle, it's pretty simple overall, and there is plenty of good info on this site and others as well.
dave