Calcium Sulfate Hemihydrate, Pure
Plaster of Paris
CAS Number 10034-76-1
EC Number 231-900-3
E number E516
Chemical formula CaSO4·0.5 H2O
Solubility in water 30g/l (20 °C)
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 increases GH but keeps KH at the same level. Use calcium sulfate hemihydrate as a mineraliser during weekly water change. Do not mix with other compounds in a bottle; in concentrated substances calcium reacts with most macro and trace elements.
Use it together with magnesium, ideally with magnesium and potassium. Some sources recommend maintaining following proportions: Ca:Mg – 4:1 – 3:1 and K:Mg – 2:1. Other sources suggest other proportions therefore the above should be seen only as suggestions and you can experiment, try different proportions and see which one works best for you in a long run.
Store in dark place, in room temperature.
Good To Know
Calcium is a macro element; it makes about 0.5% of a dry plant. Calcium is an activator of many types of enzymes, is a component of cell wall, it also plays a crucial role in regulating cell processes. Calcium is a non mobile element therefore its deficiency symptoms are usually visible in growing points and the youngest leaves. Plants absorb calcium in the form of ions Ca(2+).
Calcium deficiency is rather uncommon, possible only in very soft water.
Indicators of calcium deficiency are: severely impeded growth (also affects roots), growing points decay (in serious cases), chlorosis (on the edges or general in the form of spots), young leaves size reduction and deformation. Other sources indicate that leaves become brown. Furthermore, necrosis of points and young leaves’ edges is possible.
Calcium excess in itself is not toxic, however it makes the absorption of many elements more difficult for plants. This may cause deficiency of magnesium and boron, other sources also report deficiencies of phosphorus, potassium, iron and zinc. Therefore very hard water may require increased fertilisation of some micro elements.