Monopotassium Phosphate, Pure
Potassium dihydrogenphosphate, Potassium phosphate monobasic, Phosphoric acid, Monopotassium salt, Potassium biphosphate
CAS Number 7778-77-0
EC Number 231-913-4
E number E340
Chemical formula KH2PO4
Solubility in water 226g/l (20 °C)
20g KH2PO4+ 500ml water, 1ml solution per 100 l of tank water yields a concentration of 0.28 P and 0.1 K ppm
10g KH2PO4+ 500ml water, 1ml solution per 100 l of tank water yields a concentration of 0.14 P and 0.04 K ppm
5g KH2PO4+ 500ml water, 1ml solution will per 100 l of tank water yields a concentration of 0.07ppm P and 0.02 K ppm
90g KH2PO4 should last for about 350 days OR MORE (for a 100L aquarium). Also, please remember that KNO3 and KH2PO4 also contain potassium.
Store in dark place, in room temperature.
In order to measure the required amount you can either use a scale, a measuring jug (with milliliters), a teaspoon or a tablespoon. If you want to use spoons, it is important that you use the same spoon for all of your mixtures. The size of the spoon is not that important – it is the maintenance of the proportions of all of the ingredients that matters.
Just to give a rough guide: 1 teaspoon = approximately 5g, 1 tablespoon = approximately 15g.
What also needs to be remembered is that every chemical compound has different maximum solubility in water and that the values given above are accurate for distilled water. The maximum solubility in RO water will be slightly lower; solubility in boiled water will be even lower (if you want to use boiled water, we recommend you to boil it for 3min and than let it drop to room temperature).
It is worth mentioning that saturation of a solution of one salt will decrease the solubility of another salt added to the same solution.
Good To Know
Phosphorus is a macroelement, it makes about 0.2% of a dry plant. Phosphorus is a component of nucleic acid and phospholipids; it plays a key role in cells’ energy processes. Phosphorus is a mobile element, therefore symptoms of its deficiency occur in older leaves first; although other sources suggest the symptoms occur in the whole plant. Plants absorb phosphorus in the form of ions H2PO4(-) i HPO4(2-). The most commonly used sources of phosphorus are: potassium dihydrogen phosphate (KH2PO4) or di-potassium hydrogen phosphate (K2HPO4). The recommended level of phosphorus is 0.5 – 1 ppm; some aquarians believe the perfect level to be approximately 2 ppm. The level needs to be monitored regularly (at least during the first couple of months since the aquarium’s set up). Well-lit aquariums with CO2 injection (even in those with a big fish population) often need phosphorus dosing. The usual dosing is approximately 1 ppm PO4(3-) a week.
In planted tanks phosphorus deficiency is quite common. Often the only symptom is an impeded growth of the plants (in more severe deficiencies the growth is completely blocked). Another often occurring symptom of phosphorus deficiency is the decrease of the size of the blades. The symptoms usually occur in older leaves, but with time they can spread to the younger plants too. Leaves become dark green, purple-lilac (stems may be affected too) or retain their normal colour. In some cases, the tips of the leaves become brown and wither, sometimes they fall. Blossoming may be also inhibited. Another symptom noticeable in aquariums may be the lack of photosynthesis (no visible bubbles despite of a good level of light and CO2) and increased growth of green algae on leaves and glass.
In planted tanks excess of phosphorus is quite unlikely. Possible symptoms of excess levels of phosphorus may be a microelements deficiency, especially of zinc, copper, iron, manganese and, according to some sources, potassium. Despite of a common view, the excess level of phosphorus (3-5 ppm) does not lead to increased growth of algae.