Just because food is eaten, does not mean it's gone. Everything you put in the tank must be removed, by you, via water changes, skimming, etc. Put a weeks worth of food in your hand and think about how effective your mode(s) of export is.
I'm not saying this is definitely the problem, but I think we can agree that something is definitely wrong. Though I can't see how you could have high nutrient levels without some other symptom, like nuisance algae perhaps.
can I see a pic of the tank?