Saltpeter, Saltpetre, Nitrate of potash
CAS Number 7757-79-1
EC Number 231-818-8
E Number E252
Chemical formula KNO3
Solubility in water 242g/l (20 °C)
90g KNO3 + 500ml water, 1ml solution per 100 l of tank water yields a concentration of 1.1 NO3 and 0.7 K ppm
50g KNO3 + 500ml water, 1ml solution per 100 l of tank water yields a concentration of 0.6 NO3 and 0.4 K ppm
25g KNO3 + 500ml water, 1ml solution per 100 l of tank water yields a concentration of 0.3 NO3 and 0.2 K ppm
90g KNO3 should last for about 250 days or more (for a 100L aquarium)
Store in dark place, in room temperature.
Good To Know
Nitrogen is a macroelement, it makes about 1.5% of a dry plant. Nitrate is a component of proteins, nucleic acid and chlorophyll. Nitrate is a mobile element (can transfer from one part of the plant to another), therefore symptoms of its deficiency occur in older leaves first. Plants absorb nitrate in the form of ions NO3-, NO2-, NH4+ and urea. Water plants absorb nitrate first of all in the form of ammonium cation, as its absorption requires the least energy. Ions NH4+, however, are toxic for fish and stimulate the growth of many algae therefore are not recommended for use in planted aquariums. The most commonly used source of nitrate is KNO3 (Potassium Nitrate). The recommended level of nitrates is 5-30 ppm. The nitrate level needs to be monitored regularly (at least in the first few months since the aquarium’s set up).
Well-lit aquariums with CO2 injection (even in those with a big fish population) often need nitrate supplementation. The usual dosing ranges from 5 to 25 ppm NO3- a week.
In planted tanks nitrate deficiency is quite common. Low nitrate level (close to deficiency level) in red plants leads to intensified colours. In case of moderate deficiency usually the only symptom is an impeded growth of the plants. In case of more severe deficiencies the growth is completely blocked. Also, smaller leaves, smaller propagation and general chlorosis of older, and with time younger, leaves (indicated by light-green to yellow colour) are typical symptoms of nitrate deficiency. In more severe deficiencies, necrosis and fall of leaves occur. Leaves and stems of some plant species become red or orange. In case of some plants (e.g., watermillfoil, hornwort, ditchmoss) stem fragmentation may also occur.
In planted tanks excess of nitrate is quite unlikely. Possible symptoms of excess levels of nitrate can be visible on the whole plant. Leaves become dark-brown and blossoming is inhibited.
Potassium is a macroelement, it makes about 1% of a dry plant. This element activates over 50 enzymes, takes part in osmoregulation and in ion balance maintenance. Potassium is a mobile element, therefore symptoms of its deficiency occur in older leaves first. Plants absorb potassium in the form of ions K+. The most commonly used source of potassium is potassium sulphate (K2SO4) and potassium chloride (KCl). The recommended level of potassium is from 5 to 20 ppm a week. In planted aquariums, in which this element is not provided, there is a high likelihood of its deficiency. Tap water doesn’t have enough of this element to meet the plants’ needs. When it’s necessary to dose KNO3 to maintain a good level of nitrates, further dosing of potassium would not be necessary.
In planted tanks potassium deficiency is quite common. In case of moderate deficiency usually the only symptom is impeded growth of the plants (in more severe deficiencies the growth is completely blocked). Chlorosis of older leaves’ tips and edges, often leading to their necrosis, in more severe potassium deprivation spreads to the leaves’ blades (the main veins remain live however). In other cases, yellow, brown or white spots, also leading to necrosis, appear on plants’ leaves. Potassium deficiency also manifests itself in chlorosis between the veins throughout the whole leaf blade. Some sources also suggest symptoms such as growing points withering, fragile sprouts, poor development of root system and leaf fall (in more severe cases).
The most often mentioned effect of excessive potassium is magnesium or calcium deficiencies. Other sources also indicate manganese, nitrate, zinc and iron deficiencies. Some sources suggest that excess of potassium is harmless. Some aquarists providing high doses of potassium (20 ppm a week or more) noticed young leaves deformations and growing points withering. Such problems were particularly evident in Ammania gracilis plants.