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Dupla iron supplementation: a query
Thanks for the comment in response to my post on the APL concerning
iron levels in Kent supplements. I will be responding to some of the
comments over the next few days. I suspect George Booth is probably correct
that not all the iron which is measurable in the water column is utilizable
by plants.
My recent pondering about iron supplementation with the Kent product
led me to wonder about the rationale for the Dupla system of trace element
(especially iron) supplementation. Unless I am mistaken, Dupla drops, with
their 1180 ppm iron (information from George Booth), are added in such small
volume that they contribute very little to the total iron concentration in
the tank. Assuming .05 ml per drop and 4 litres / gallon, addition of a
daily dose of 4 drops to 85 gallons (again, chosen from an example by
George) would raise the iron concentration of the tank by only .0007 ppm [4
x .05 x 1180 / (85 x 4 x 1000)]. Even a week*s, daily additions would
contribute only .0049 ppm to an 85 gallon tank, i. e., only 0.5% of 0.1 ppm,
considered by many a reasonable target concentration or iron. Thus, tanks
which are run according to the Dupla system must derive most of their from
products other than the drops. Information posted on the APL indicates that
the principal other iron sources among the Dupla products are (1) DuplaPlant
tablets and (2) laterite.
But I do not understand the rationale for adding iron in both the
tablets (with water changes) and daily drops. If the plants need the drops
for the extremely small amount of iron they contribute, what is the purpose
of the iron in the tablets? If I am not mistaken, information from previous
APL posts indicates that both the drops and tablets contain chelating
agents, so the iron in both products is apparently chelated. Is this
correct? Dupla says that the purpose of the drops is to add materials which
are either unstable or sufficiently toxic that they cannot be dosed to last
more than a day or so at a time. The chemical analysis of the drops
suggested that iron-EDTA is the principal, if not the only, ingredient. Is
it the iron which is unstable or toxic at higher doses? (As noted above, the
quantity of iron added with the drops is way below the levels maintained in
most tanks, so clearly the iron in the drops is not toxic.)
Thus, my basic question is, why is iron added both with the tablets and
with the daily drops, especially when the quantity of iron added with the
drops is so miniscule?
Laterite is the other, principal iron source. Does anyone know how much
of the iron in laterite escapes to the water column? Any data on iron
concentrations in aquarium water with laterite which has not received
another source of iron?
I am probably missing something here, somewhere. Can anyone enlighten
me?
Richard Denney.