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Re: Reference Solutions
About 3 weeks back (my current reading backlog for the APD) George
suggested the possibility of making reference solutions to calibrate
test kits. This is a pretty good idea (where did I hear it before? ;-)
The problem with using teaspoon measures for common powders is that I've
found that the bulk densities for several chemicals can vary
considerably especially calcium carbonate. I do have a triple beam scale
and so its not difficult for me to weigh stuff under 600 grams with a
resolution of 0.1 grams.
I would recommend folks to search for postal scales. Many kitchen scales
are good for weighing quantities with resolution of an ounce or two. If
you go to a place like Staples (do that have that in the USA?), you can
get a wide selection of electronic scales that weigh down to 1 gram. To
get better quality electronic scales at a reasonable price, you should
check the yellow pages for jeweller supplies. Those guys have to weigh
gold very accurately and so its no problem to get a small electronic
scale that will weigh with 0.01 gram resolution up to several grams.
Chemistry supply catalogues give you a wider selection of large range,
high resolution scales however I don't think the average hobbyist needs
that kind of equipment for the price. Another store that sells cheap
scales are so-called head shops where they sell paraphernalia for pot
smokers. (ok, ok; jest if you must)
You can calibrate your small postal scales using coins. A dime is two
grams and a quarter is 5 grams. A dollar bill is 1 gram.
If you need to prepare 1 litre solution with 1 gram of a chemical but
you can only weigh accurately to about 10 grams, weigh out 10 grams and
put it in 10 litres of water. Then you can accurately save 1 litre of
that water. Such reference solutions are probably only accurate within
5-10% however this is quite sufficient for calibrating a test kit which
has a measurement error at the lower end of 50-100%.
Kinds: postal, kitchen, jeweller, chemistry, "specialty".
Sources: yellow pages, jewller supplies, Staples etc., head shops,
hydroponics supplies, department stores, stationary, office supplies.
Of course, if what you want to do is end up with a known solution in
your aquarium, you can dispense with the test kit entirely and simply
add known dosages of potassium, magnesium and calcium. You can also dose
chelated Fe in this manner and get very low concentrations which you
dose as often as you like. (say 0.001 ppm Fe added each day) With a very
low concentration like that, you could add it every day with little fear
of a final concentration ever approaching 0.1 ppm.
If you want to hit 0.1 ppm Fe final concentration closely, well then you
need a good test kit.
How important is hitting the magic 0.1 ppm of Fe? I don't know. I know
I'm fairly happy with a much lower concentration but I have substrates
that provide iron to most of my plants. The floating plants like
Salvinia probably don't get enough but my Java Fern seems to grow just
fine. Different plants may have different needs. I suspect I could push
my growth rates higher by using a daily or weekly dosage of trace
nutrients but I don't really need more growth. I find it difficult to
find the time to do water changes, trimming and take my surplus to the
store. Those with more spare time, can probably do quite well farming
plants for sale and should push their growth rates wherever possible.
If your primary concern is getting your algae under control, then I
don't think you should be pushing the Fe too much at all. Others may
have differing opinions on this point. I would say, get your other
nutrient concentrations up (K, Mg, Ca, CO2), sufficient nitrogen (not
too much) and a little bit of chelated Fe (experiment!) but do not
overdose. I bet you can get excellent macrophyte growth with Fe in the
range 0.005 - 0.05 ppm so I would start with a daily addition of 0.001
Steve Pushak Vancouver, BC, CANADA
Visit "Steve's Aquatic Page" http://home.infinet.net/teban/
for LOTS of pics, tips and links for aquatic gardening!!!