I have an AZoo Bio-Denitrator, which has worked great for about six months. My nitrate levels were almost undetectable until about two weeks ago. I noticed my levels go from zero to 10ppm in a matter of about ten days. Now my levels are around 20ppm. I have increased my water change frequency to compensate for the rising nitrate levels. It seems as if the unit has become ineffective. Does anyone have any experience with this equipment? Does anyone have a replacement recommendation?