Hi all,
[quote="humdingerx, post: 390317, member: 13093"(or if the red ones are just dyed??)......could get some cheap iron enriched red clay?[/quote] Any red clay will do, it isn't dyed it is just that the iron is in the oxidised FeO3 (ferric) form. Most blue-grey clays are also iron rich, they are initially grey because they have been water-logged, and the iron is the FeO(H)2 (ferrous) form. This is also why bricks are typically red, when you fire the clay any ferrous hydroxides, or oxides, are coverted to ferric (Fe(III)) oxide.
The reasons that the clays are iron rich are two fold, one reason is that iron Fe++(+) is the most strongly bound cation, and the second is that iron oxides and hydroxides are insoluble, and once they formed they can't be leached. This is why ancient tropical soils in area of high rain-fall are "lateritic", only the insoluble aluminium, silicon and iron compounds remain.
That is also why the amount of iron in the clay isn't particularly relevant, this is because it is all insoluble unless you have an acid, anaerobic sediment (with negative REDOX values) where microbial reduction of Fe(III) can occur.
Adding a chelated form of iron to the water column (FeEDTA etc.) is a more efficient way of adding plant available iron, although if you have a fairly mature planted tank its likely that some iron will become available in the rhizosphere in the substrate.
There is a good article on <"
iron"> via the ever erudite "Skeptical Aquarist".
cheers Darrel
