Makes it easy to monitor the ammonium/ammonia level in fresh and marine waterAmmonium and ammonia mainly arise from fish waste. They are converted into each other depending on the pH value. While ammonium is mostly harmless, ammonia is toxic to fish. The sera NH4/NH3-Test allows monitoring the total concentration of both (the actual ammonia level can be calculated according to the pH value the using the included chart). Ammonia is the natural waste product of fish metabolism and will accumulate in the aquarium to toxic levels, killing the fish. Fortunately, beneficial bacteria in the biofilter will break down the toxic ammonia. However, there are two forms of ammonia that occur in aquariums: un-ionized ammonia (NH3), which is the toxic form, and ionized ammonium (NH4+), which is essentially non-toxic. The higher the pH and temperature, the more toxic ammonia becomes which is why it is really important to monitor cichlid and marine tanks closely. In case of acute danger, dose your aquarium with sera toxivec (freshwater). Sufficient for approx. 60 measurements. Purchase with confidence knowing your test kit will last! Expiry 02/2022!