Sorry, I don't measure the nitrate levels in any of my tanks. A friend did about 10 years ago in the 50K and found different levels in different areas. Since I don't add fish very often there is no need. The fish in the 50K have in many cases been in the tank since 1994. Prior to that they were in the same water conditions in my other tanks. Living in the country I have had no water problems with my fish possibly because the water has remained very stable.