Nitrates can cause cloudy water and sanitiser demand, but levels up to 25 ppm have been tested without causing any problems. Some sources of nitrates are fertilisers, human and/or animal waste, debris and lightning. Nitrates do not break down naturally, and if it is established that they are the cause of a problem, must be removed by partial drain.

NOTE: Nitrates cannot be precipitated out of solution (almost all nitrates are water-soluble) and cannot be oxidised (the nitrogen in nitrates is already in its most oxidised form).