Potassium Sulfate, Pure
Sulphate of potash
CAS Number 7778-80-5
EC Number 231-915-5
E number E515
Chemical formula K2SO4
Solubility in water 111g/l (20 °C)
90g K2SO4 + 500ml water, 1ml solution per 100 l of tank water yields a concentration of 0.8 K ppm
50g K2SO4 + 500ml water, 1ml solution per 100 l of tank water yields a concentration of 0.45 K ppm
25g K2SO4 + 500ml water, 1ml solution per 100 l of tank water yields a concentration of 0.22 K ppm
K2SO4 should last for about 250 days (for a 100L aquarium), it’s worth remembering that KNO3 and KH2PO4 also contain potassium.
Store in dark place, in room temperature.
Good To Know
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.