another thing about nitrate test kits is that if they have been sitting for a while they will read 0ppm no mater what your results are. this is because there is a heavy metal in the solution, i think its zinc, and after some time it seperates and sink to the bottom of the bottle. the zinc is needed to get readings. so you need to shake the life out the bottom to "remix" it.
i personally would trust the api test kit.
i personally would trust the api test kit.