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Re: Lignin sulfonate. Is there a chemist in the house?

Andrew asks for a comparison of lignin sulfonate and other commercial
chelators for Fe.

I will hazard an educated guess that lignin sulfonate chelated Fe will
work fine as an hydroponic method for providing iron to aquarium plants.
No one has suggested there are any side effects about the chemical and
there are plenty of water quality experts reading.

Lignin sulfonate may not be as persistent as EDTA or DTPA but you could
certainly adapt it especially if you were dosing every day or perhaps
even once a week. With a good test kit; you should be able to determine
how much demand there is for replenishment of the iron. Shoot for the
same goal: 0.05 ppm Fe I would guess. Some aim for 0.1 ppm.

I suspect that this is very similar to the method of providing iron in
solution by having peat and soil (most soils contain iron) in the
substrate. The lignin sulfonate or humic acids persist in the water and
the Fe enters and leaves solution freely but maintains some low steady
state concentration. With peat water, you need to exchange the water
frequently enough to keep the humic levels (which establish the Fe
availability) reasonable.

As with PMDD and every other commercial nutrient dosing method; the
circumstances of water supply, substrate, bio-load, feeding pattern,
nutrient availability, lighting and plant load will dictate the demand
for nutrients and so it is always a matter of trial and error to
establish the correct protocol for dosing. (at least without benefit of
tissue sample analysis!)