Yes it is and here is the definition: Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is of one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare, and iron(II,III) oxide (Fe3O4), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main source of the iron for the steel industry. Fe2O3 is paramagnetic, reddish brown, and readily attacked by acids. Rust is often called iron(III) oxide, and to some extent, this label is useful, because rust shares several properties and has a similar composition. To a chemist, rust is considered an ill-defined material, described as hydrated ferric oxide.
It is my understanding the it is the iron that dissolves into the water it what feeds algae but I am not a chemist. You see iron is plant food as well.
