There are no such things as nitrate factories. Just lazy reefers parroting what they have heard when they mostly do not understand what is going on. How is it biologically possible to create nitrate out of nothing like a factory creates something out of nothing? There is no way to just produce it out of thin air. If you have high nitrates, then you aerobic filtering is working correctly, you just have no anaerobic areas/filters to turn the nitrate into nitrogen gas and thus fully complete the N cycle.