Jeffrey Funk;122509 said:
My experience with Fe analysis by ICP-OES is that [Fe] in the water column does depend upon the type of Fe chelate dosed. People that dose Fe(EDTA) often have measurable Fe in their aquarium water (>0.01 ppm) while those people who dose Fe(Gluconate) often times have much lower measurable Fe in the aquarium water, even if they dose the same amount during each time.
Because of this, it's not always clear that a low [Fe] in the aquarium means that you are not dosing the correct amount of Fe. You really need to watch your plants and see how they are growing...
Adding even more to this quagmire, we have variation in the alkalinities from user to user.
This makes the chelators behave differently.
Fe Gluconate will act differently in my low KH of 20 ppm vs another user who's KH is 140 ppm.
DTPA seems pretty stable over the pH/KH ranges we often see.
I think overall, we are left with dosing and
know amount and chelator type and then observations of the plant's growth, color, sheen, form.
Amount (mass) and chelator types offer a known standard baseline to compare.
If you choose an upper bound, say a very high light tank, plain sand to remove any sediment sources, CO2 rich, faster growing stems(a wide variety of species), non limiting feerts, good algae eaters, water changes daily or often, then you could see what an upper target would be.
From there, pretty everyone would dose LESS.
This way we'd have an upper bound, and then the lower is obviously no trace dosing of Fe at all.
Everything else should fall in between that.
My 120 is a pretty good canary in the coal mine for this, but I have ADA AS which is rice paddy soil pretty rich in Fe.
If I had plain sand, then it would be ideal.
But I have in the past.
Plant growth studies suggest an order of magnitude higher than what I dose, but I was never sure what Bill Haller did as far as frequency. I could ask him if he has not retired in the near future.
I'm adding about 1-2 ppm a week total.
I add a mix of chelators, the Gluconate, DTPA and the ETDA and my KH is low.
The differences are subtle for nice plant health responses for Traces.
Sheen on the leaves is the biggest indicator I look for.
Daily seems to do a little better than 2x a week for many stem plants, but less so for others.