Makes it easy to monitor the nitrite level in fresh and marine water. Nitrite (NO2) is among the most toxic substances for fish in aquariums. It can enrich in the water in case of insufficient biological filtration. The sera NO2-Test allows monitoring the nitrite level in fresh and marine water easily and reliably. We recommend using sera bio nitrivec (freshwater), sera marin bio reefclear (marine water) in case of slightly elevated nitrite levels. In case of severe nitrite problems, sera Nitrite-minus quickly provide help. Sufficient for approx. 75 measurements.