its low levels in the tap. I would expect established filters to be able to easily handle that. I would consider the tank over filtered and not heavily stocked, so I would be surprised if the filters were having a hard time. Plus this reading was higher then what is coming out of the tap. The prime isn't causing any problems, my original question is if it interferes with the nitrite testing kit. Otherwise there is something weird going on with this tank, which seems to be the case.