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 

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?


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 

[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