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iron in Kent supplements
I will state my conclusions first, so that those who are not interested in
the details can avoid them in the remainder of the post. Anyone who is
interested, please check the calculations. Am I way off base?
My conclusions:
1. My measurements of the iron concentration in Kent freshwater supplements
(contain chelated iron, potassium, magnesium, potassium and other trace
elements, but no nitrate or phosphate) yield approximately 2000 ppm, which
is reasonable considering the value of 1180 ppm in Dupla drops (reported by
George Booth by a much more sophisticated test). If my value is correct, use
of the Kent supplement at the dosages recommended on the bottle will almost
certainly result in an initial iron concentration in the water column at
least 14-fold higher (and as much as 42-fold higher) than that which experts
on the APL recommend for plant tanks (.1 ppm). This estimate is based on the
use of an admittedly crude SeaChem iron test kit. However, the measurements
were done multiple times, each time in duplicate, using the .5 ppm iron
standard solution provided in the test kit. The estimates are, however,
compatible with the color chart provided with the kit.
2. To use Kent supplements on a daily basis, in an attempt to keep the iron
concentration near .1 ppm (in a tank whose iron concentration is already .1
ppm), I estimate that a reasonable dosage to try would be 3-4 drops per day
for an 85 gallon tank. Determination of whether this dosage is satisfactory
for a given tank could only be done by noting whether iron levels go up or
down over a period of time. I estimate that establishing a concentration of
.1 ppm in 85 gallons of iron-free water should require about 1/8 tsp per 30
gallons of water, or about 1/8 th the _minimum_ concentration recommended by
Kent.
3. Since neither Kent nor most of the other companies reveal the
concentrations of other micronutrients in their products, it is not clear
whether reducing the dosage of these products drastically (about 20-fold on
the case of Kent) will provide sufficient quantities of the other
micronutrients in the products. I suppose one can only watch the plants and
see if deficiencies develop over time.
4. Despite my use of the Kent product (blush), it is obviously better to
follow the advice of the experts on the APL and make up your own trace
ingredients so you know what and how much you are adding. PMDD anyone?
Background.
Considering the extensive discussion of trace element supplement products in
the Archives, I thought someone might be interested in some home
measurements I have done on the relatively popular Kent freshwater
supplements (iron and other trace elements, no phosphate or nitrate). I have
been using these for trace element supplementation along with Tetra Crypto
tablets in the substrate (iron-EDTA plus potassium) in my 75 gallon, heavily
planted tank (DIY CO2, GH 2.5, KH 4.5; pH about 6.8-7.0; 240 watts good
fluorescent light, 12 hr/day). It is about 2.5 months old.
The instructions on the Kent bottle say add 1 to 3 tsp per 30 gallons
initially and the same with every water change. There is clearly ambiguity
here, since if the subsequent additions are based on the total tank volume,
the iron concentration will clearly build up, unless the plants use up the
difference in the meantime. SInce there is no standard with respect to how
much water should be changed and how often (and no recommendation on the
Kent bottle), there is lots of room for confusion. In settling in, my 75
gallon tank developed some algae problems, at least some of which I
attribute to phosphate in the tap water (1 ppm; thanks, water company). As
detailed in a previous post, I resolved the phosphate problem (and hard
water, organics, salt etc.) by going to reconstituted RO water, and the tank
is doing much better. In particular, there is is now almost no hair algae.
Some thread algae and a small amount of "staghorn" algae remain. Incidently,
my improving algae situation appears to be yet another example of drastic
reduction in hair (and other) algae resulting from elimination of a primary
nutrient problem (in my case phosphate concentration). Other beginners, take
note! Currently, the remaining algae does not appear to be spreading to new
leaves, and all plants look healthy and are growing steadily.
In researching the the algae problem in the archives, I noted that George
Booth has indicated that he sees filamentuous algae problems when iron
levels exceed about .15 ppm. Measurement of my aquarium water suggested that
thanks to my addition of Kent supplements, I had achieved an iron
concentration of .5 ppm. This and all other measurements reported here are
based use of a SeaChem iron test kit. (I have run all tests in duplicate
using dilutions of their .5 ppm standard iron solution as a standard curve.
I would estimate my results to be accurate to about plus or minus 25%).
Since Kent does not say how much iron is in their supplement, I measured
iron concentration on a dilution (1/4 tsp in 2 quarts of water) and got 1.2
ppm, which yields an estimate of 2000 ppm iron for the undiluted supplement.
(Incidently, Kent says that this is chelated iron. My results are consistent
with this, since the SeaChem test claims to measure free iron (fast color
development, 10 min) and chelated iron (slow color development, or 45 min).
The color of the standard in the SeaChem kit develops very rapidly (roughly
stable between 2 and 45 min) and is probably free iron, while the color from
the Kent supplement develops slowly to a reasonable plateau by 45 min.) A
value of 2000 ppm for the Kent product is reasonable, since Tetra Flora
pride lists .14% (1400 ppm), if I recall correctly, and George Booth's
electron emission spectroscopy measurement of Dupla 24 drops yielded 1180
ppm.
[Incidently, has anyone resolved the question that arose in the APL as to
whether these test kits measure both Ferric (+3) and Ferrous (+2) iron? I
have not seen a definitive statement on this point.]
So, my SeaChem test data suggest that Kent has about 1.5 times higher iron
concentration than Dupla 24 drops. (This result is also consistent with
Kent's claim on the bottle that it has a higher iron concentration than
competing products.) Now, assuming 2000 ppm for the straight stuff, adding
the recommended 1 to 3 tsp per 30 gallons (1 tsp is 4.8 ml; 30 gallons is
roughly 4 x 30 or 120 litres) should result result in a final iron
concentration of about 2000x4.8/120,000 to 2000x3x4.8/120,000 ppm, or .8 ppm
(1 tsp) to 2.4 ppm (3 tsp), which is obviously much higher than the .1 ppm
George recommends. This is of course not added on a daily basis, but only
after every water change, however often that is done. Nevertheless, my data
suggest that following the instructions on the Kent bottle result in iron
concentrations which are much higher than .1 ppm, at least initially.
When I discovered the high iron concentration in my tank, I changed 30% of
the water twice, and got the concentration down to approximately the
recommended .1 ppm. I decided to see whether I could maintain the iron level
near .1 ppm by adding 1/7 the Kent's recommended, lower, weekly dose each
day (i.e., 1/2 tsp per day for my 75 gal tank). On day 3, following
additions of 1/2 tsp on days 1 and 2, the iron concentration in the tank had
risen to about .15 ppm, perhaps a little more. Obviously, 1/2 tsp per day
was more than the plants were removing. The question remained, how much do
they remove?
Unfortunately, I have been unable to dig out of the archives any estimate of
how much iron is actually consumed (or otherwise disappears?) in a heavily
planted tank on a daily or weekly basis. I realize that this will be highly
variable and depend on the plant (and algae) mass, and perhaps on the levels
of previously stored iron. I have therefore estimate daily usage of iron
based on the dosage of Dupla 24 drops (1180 ppm iron) George Booth says he
routinely uses for his 85 gallon tank (4 drops per day) to keep the iron
levels around .1 ppm. Less of the Kent supplement (1180/2000x4 = 2.4 drops)
should provide the same iron dose. Assuming a reasonable drop size of about
.05 ml, this would suggest that Kent should be added at somewhere around 2.4
x .05 ml or .12 ml per day. Since 1 tsp is 4.8 ml, this would be only
.12/4.8, or .025 tsp per day of the Kent supplement, or about 5% as much as
the 1/2 tsp per day I calculated based on distributing Kent's _minumum_
recommended dose over a week (seven equal daily doses)!
Clearly my results are based on a relatively rough test (the SeaChem iron
test kit). However, unless my calculations are grossly wrong (it has
happened before!), it seems that persistent use of the Kent supplements
according to the recommended dosage will result in excess iron
concentrations. If excess iron concentrations contribute to algae problems,
consider scaling way down on the dosage!
Hoping the calculations are right in Dickinson, TX
Richard Denney