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[APD] Driftwood, tannins and calcium deficiency

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

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