Nitrates (to me) are a relative thing. You see a LOT of people swear up and down that high nitrates kill fish. Then you go and look at real world water quality of places doing well with rays and (I kid you not) you can see levels over 1000ppm.
High nitrates are a result of natural process. Feeding animals means creation of ammonia, broken down into nitrite, then nitrate. Nitrate can build up in the system several ways - the most common being biological debris hainging out in dead spots in your water.
In short, I don't worry about them as much as most will.