You'd do your fish a lot of favors if you did an true Water Change and Gravel clean.
There aren't too many ways that you can eliminate nitrAte, but the easiest one is to do a water Change, which means that you remove water from the tank and replace it with fresh, treated water.
It sounds like your ammonia and nitrites are in good order, but everything else needs handling.
My understanding is, nitrAtes effect your fish internally, so its effects generally aren't noticed externally until it's too late.
I'm sure other, more experienced people on this board will have far more accurate and complete information for you.
But doing a water change in the mean time probably wuoldn't hurt.