Iron(II) sulfate or ferrous sulfate are salts with the formula FeSO4.xH2O.
Known since ancient times as copperas and as green vitriol, the blue-green heptahydrate is the most common form of this material, which is used medically to treat iron deficiency. In algae and plant cultivation, it does the exact same thing, enriching the culture with iron and improving the absorption of oxygen. It also has a wide range of industrial applications.
All iron sulfates dissolve in water to give the same aquo complex [Fe(H2O)6]2+, which has octahedral molecular geometry and is partially magnetic.
Read about the preparation of ferrous sulphatic acid for spirulina cultivation.