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Re: iron and TMG etc
On the subject of high Fe vs low Fe, Scott H. wrote:
"This would be fine if "commonly advised approaces" were all the same
and no one cared about the differences. But I think some do -- at
least, as a matter of interest if not a matter of critical tank
management."
Indeed....
Tom's approach, maintaining high levels of iron, obviously works for him,
and would seem to be supported by the material I quoted last night from
Allgayer & Teton. For those who are unfamiliar with this book, it was first
published in 1986 as Plantes et Decors d'Aquarium and then translated and
published in English the following year (1987) by Ward Lock Limited, London.
Somewhat dated, it is still, in my opinion, one of the best aquatic plant
books ever written.
Dupla's The Optimum Aquarium was first published in 1977 and was extensively
revised in the English language edition I have, which dates from 1986.
So both books are pretty contemporary with one another.
Roger's approach seems to follow Dupla's recommendations, at least as far as
nutrient levels go. They obviously work for him (and for me and thousands of
others who have been following Dupla's methodology since 1986).
One variable which _may_ make a difference here is the amount of light a
system receives. Allgayer & Teton make note of the intensity of tropical
sunshine and also give ranges for the amount of light hitting the leaves of
plants underwater:
"Natural conditions, slightly overcast sky - 15,000 to 20,000 lux at midday"
"Under 12"-15" of water - 700 to 3,000 lux"
"In shady areas, under 12"-15" of water - 150 to 500 lux"\
They provide a table giving the range of light required by a number of plant
genera, with optimum levels highlighted. According to their recommendations,
only Sagittaria, Cryptocoryne, Marselia and Microsorium have "optimum"
levels below 800 lumens/sq meter. The majority of other plants listed have
"optimum" levels in the range of 800 - 2,000 lumens/sq meter, with the sole
exception of Myriophyllum, which needs approximately 3,000 lumens/sq meter
for optimum growth.
Dupla also goes into some detail regarding light, both in nature and in the
aquarium. The most up to date information from Dupla regarding details of
lighting are apparently contained in the article "Correct Lighting for
Aquariums", AQUARIUM HEUTE 3/94. I don't have that issue, so I don't know
how much their recommendations may have changed since ther publication of
The Optimum Aquarium in 1985 . The material currently on Dupla's website is
pretty general and while there is a 1987 article from AQUARIUM HEUTE, it
deals with marine aquariums and focuses more on available hardware than on
theory.
In the most recent version of Dupla's 10 Golden Rules for the Optimum
Aquarium, posted on their website, they state:
"Light is the aquarium's engine. It regulates the nutrient requirement,
produces oxygen and also controls the discharge of by-products and
metabolism products."
What they had to say (in 1986) is still pretty interesting:
3.1.2 Aquarium-specific Lighting
[on the amount of light]
"...What we are however also looking for in this respect is that during the
day the aquarium water reaches an optimal oxygen content. This is in the
neighbourhood of 100% saturation.... In additioon to that, close to 100%
saturation during the night, is necessary as plants require a good deal of
oxygen, and if we did not obtain this through correct lighting, we would be
facing possible catastrophic consequences."
3.9.1. Strength of Light
"The strength of light, and light temperatures, which we have measured in
nature prompt us to correct some classic ideas. For example, we found
Cryptocorynes, which have always been considered a shade plant, in very
sunny as well as very shady places. The difference in Lux was between 50 and
90,000 Lux. These plants grew in the darkest part of the stream at a point
where the depth was 3.5m. It would of course be wrong to conclude that an
aquarium does not need stronger light."
6.4 Notes on Lighting
"1 - Strength of light: 30-50 lumens per liter (120-200 per gallon)"
"2 - Temperature of light: ...5500K...."
"3 - [Time]...... 10-12 hours..."
"4 - Earlier recommendations in watt per liter have become incorrect because
of the different types of lighting.[they prefer to use the term Lumen]"
<finis>
I think the most telling point in the Dupla material is the comment about
100% oxygen saturation. Get to this point and your plants will "pearl"
indicating that the rate of photosynthesis is faster than the water's
ability to absorb it.
Dana Riddle has written an excellent article on light and photosynthesis
which appeared in the Summer 2001 issue of PAM, and Ole Pedersen, Claus
Christensen and Troels Andersen wrote another great article on the
interractions between light and CO2 and the growth of aquarium plants, which
has appeared both in TAG (Vol 14 No 1) and PAM (Spring 2001). I think that
both of these articles touch on issues which have to be considered when
deciding on "how much" of any particular nutrient is appropriate in an
aquarium.
I don't think you can isolate iron (or any other nutrient) out of the "big
picture" when you are discussing appropriate dosing levels in an aquarium.
It really makes me nervous when I see people rattle off a bunch of numbers
as recommendations with only a cursuory knowledge of the complete system
those numbers are going to be applied to. Especially when those
recommendations seem to come off the tops of their heads and don't seem to
be based on any quoted reference.
But given the tendancy most of us have to rely heavily on empiricle rather
than on experimental results, I don't think we know the answer yet. Maybe
Diana Walstad will tackle it. It shouldn't be too difficult to do, and might
be very interesting especially if it followed the same procedures outlined
by Pedersen et al when describing their experiments with the growth of
Riccia.
James Purchase
Toronto