[APD] Driftwood, tannins and calcium deficiency

[Jeffery Ludwig <jeff at rockytop_net>]

> Question: Does the leached tannins chelate Ca/Mg
> rendering it useless to the plants but still can be
> measured by GH and Ca-tests?

No.  Chelating agents hold a chemical in a particular oxidation state.
For example, the iron in our trace additives is Fe2+.  When exposed to
oxygen (in water or air), iron is stripped of electrons and converted to
Fe3+, usually in the form of rust, Fe2O3.  The Fe2+ is higher in energy
and what our plants prefer.  The cleating agent encapsulates the iron
molecule and prevents oxygen from attacking it, holding it in a form
useful to plants.

Calcium is a group IIA chemical which is only stable in a +2 oxidation
state, so it does not need the protection a chelate can offer.  Chelates
are by definition weak associations that can be broken fairly easily --
I would not expect a tannic - metal complex to ever be strong enough a
plant could not break it.  The type of reaction you need to worry about
are precipitation reactions, such as the Fe + phosphate reaction.  These 
strongly bound salts would be fairly inaccessible to plants.

Jeffery Ludwig
http://www.rockytop.net



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