Nick

I've just got a Nutrafin/Hagen test kit for Fe. I've stocked up on the Flourish range for a new tank to be set-up tomorrow, and I'll be using your Fe supplement, Flourish, and Flourite for Fe supplementation. My test kit measures what it calls free, non-chelated iron and chelated iron. What's the difference-geochemically Fe is present in it's reduced form, Fe2+, and Fe3+, the oxidised form. As I see it the redox potential in my aquarium isn't going to result in Fe2+ being freely available to plants (unless something bad happens!), hence the use of supplements. Any idea what free, non-chelated iron is, and more importantly, given your Fe supplement isn't chelated Fe3+, which reading should I be using to assess Fe levels available to my plants when using your supplements (i.e. to test for complexed Fe2+)? Is it free or not!?!

Nick

Seachem

I think you already have this down but merely want to make sure and perhaps offer the information to anyone else reading the thread.

Iron will be in two oxidation states: ferrous having a +2 charge, or ferric having a +3 charge. Ferrous iron, the preferred iron form, is soluble in water at any pH. Ferric iron, however, is only soluble below a pH of around 5.5; but if the pH is higher than 5.5, the ferric iron will become insoluble and precipitate, settling in the root zone. Once this occurs foliar adsorption becomes impossible.

To overcome this precipitation, many products employ a chelate of ferric iron: iron-EDTA. While this does keep it soluble, it has a couple of drawbacks with respect to foliar uptake. Iron-EDTA bonding is very strong, thus very little of the iron will be available to the plants over a given time frame. Also, physiological energy must be expended by the plant in order to extract the ferric iron from the iron-EDTA and then convert (reduce) it to a ferrous form.

Seachem's appraoch is different in that we use a complex (not chelate) of ferrous iron in F Iron. F Iron is an iron gluconate which offers a more easily utilized ferrous form of iron that remains soluble in solution. It also offers an additional source of carbon to the plants.

I see where testing our iron might draw question given the description "free, non-chelated iron and chelated iron". F Iron would fall under the free, non-chelated iron assuming they are referring to the difference being the use of EDTA chlelates or not. F Iron is not a chelate.