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Re: chemicals and dosing
>
>Date: Thu, 3 Apr 1997 23:58:12 -0500 (EST)
>From: Tim Mullins <tmullins at telerama_lm.com>
>Subject: PMDD: Sources and Doses Round 2
>
>In response to questions on PMDD, here's
>an update on my post on where to buy PMDD
>(poor man's dosing drops) and how to use it.
>Hope this helps (many thanks to those who made
>comments, sorry this has gotten so dang long):
>
>
Thanks Tim for the complete and interesting post. I have set it aside for
study when I get the time. In the meanwhile, I thought I would share my
draft writeup that is related to the general concept of dosing -- involving
trace element mixes, commonly available chemicals and use of tools like
measuring spoons. I thought people might find it useful (I hope the columns
are not messed up too badly and that people do not take offense to the use
of "American" units <g>)
--------------------------------------------------------------------------
Determining the Concentrations of Chemicals Added to the Aquarium
Introduction
Chemicals are often added to aquariums to provide food for plants or to
establish other chemical parameters. Added nutrients may be macro nutrients
(e.g. potassium (K), magnesium (Mg), calcium (Ca)) or trace elements. In
some cases, Nitrogen (N) may also be needed when the plant's requirements
exceed the available supply or when plant growth is intentionally pushed.
The chemicals may also be needed to correct nutritional deficiencies. In
addition, bicarbonate levels in the aquarium water are often modified to
achieve desired pH. With a pH controller, this will help establish
particular CO2 concentrations in tanks with CO2 injection.
Sometimes chemicals are provided through commercially prepared nutrient
solutions, pH buffers or KH "builders." However, the aquarist may want to
create his or her special brews to replace or supplement the commercial
products. Fine tuning may be useful in order to account for one's local tap
water and particular aquarium conditions. This discussion does not
extensively focus on the specific circumstances indicating when and why one
adds these chemicals to the aquarium. This has been discussed elsewhere.
Instead, the focus here is on determining the concentrations and achieving
target levels.
Chemicals for the aquarium can be found as dry ingredients (crystals or
powders), or in liquid form (solutions). Many useful chemicals can be found
in the grocery or local pharmacy. The dosing approach described here can
involve a concentrated "stock" solution or dissolving the chemical in a
small amount of water and then adding the potion directly to the aquarium.
Applications are included for adding macro nutrients (N, K, Mg, Ca),
achieving target iron concentrations using trace element powders and
increasing carbonate hardness (KH) or general hardness (GH). Avoidance of
excess concentrations is discussed.
Terminology and Computational Procedures
Concentration units of chemicals in the aquarium are often expressed in
parts per million (ppm), for example milligrams of nitrate per 1,000,000 mg
of solution. (A liter (L) of water weighs 1000 grams (g) or 1,000,000 mg,
and so one ppm is one milligram per liter). One ppm is also the same as 1 g
(1,000 mg) per 1,000 L.
For Americans and others who may not be comfortable with the metric system
or still think about their tanks in terms of U.S. gallons, concentrations
can also be expressed in other units. Multiples of 10 gallons is a useful
volume. For 1 gram of soluble material, the concentration in 10 gallons of
water can be determined by simple arithmetic. Because 10 gallons is 37.85 L,
then 1 gram (g) / 10 gallons is 26.4 ppm. For 50 gallons, one gram creates
5.3 ppm.
Often we are not interested in achieving the concentration for a particular
chemical compound (like table salt, NaCl), but separately for its chemical
constituents or ions (i.e., the Na+ or Cl-). This is also true for the
components of nutrient salts, like Sodium Nitrate (NaNO3) or mixtures of
trace elements. In general, specific elements or ions represent a fraction
of the entire chemical. For example, Chloride represents 61 percent of the
weight of table salt.
If the concentration of Fe in the trace element. mix is 7 percent, then one
gram of trace element powder added to 50 gallons of water is simply (0.07) x
(5.3) = 0.37 ppm.
We can also work backwards to determine the amount of chemical needed to
achieve a particular target concentration. With trace element powders, iron
is often used as the indicator variable and tells the aquarist if all other
trace elements are in proportion. For this purpose 0.1 ppm Fe is used.
To determine the achieve 0.1 ppm Fe from the trace element powder, the
number of needed grams, G, in our example volume of 50 gallons of water is:
(0.7) x (5.3) x G = 0.1, so, G = 0.27
In other words, approximately 1/4 g of this trace element powder is needed.
The same principle can be used to determine the amount of any compound (e.g.
table salt) needed to achieve a desired concentration of any ion or element.
Example Chemical Concentrations
The following table shows the percentage of various ions in different
compounds and the resultant concentration for different constituents from
dissolving 1 gram of the compound in 50 gallons of water.
------------------------------------------------------------------------------
Compound ion or percent (p) concentration (ppm)
element of compound resulting from
1 g in 50 gal (189 L)
------------------------------------------------------------------------------
Sodium Nitrate nitrate 73 3.9
(Nitrate of Soda) nitrate N 16 0.9
NaNO3 sodium 27 1.4
Ammonium Nitrate nitrate 78 4.1
NH4NO3 nitrate N 17.5 0.9
ammonium 22.5 1.2
Ammonium Chloride ammonium 34 1.8
NH4Cl
Sodium Bicarbonate bicarbonate 73 3.9
(Bicarbonate of Soda) sodium 27 1.4
NaHCO3
Potassium Chloride potassium 52 2.8
(Muriate of Potash) chloride 48 2.5
KCl
Potassium Nitrate potassium 39 2.1
KNO3 nitrate 61 3.2
Calcium Carbonate calcium 40 2.1
CaCO3 carbonate 60 3.2**
Magnesium sulfate magnesium 10 0.5
(Epsom salt) sulfate 39 2.1
MgSO4*7H20 water 51 2.7
--------------------------------------------------------------------------
* concentration = 5.3p / 100
**Note: the carbonate is converted into bicarbonate after the CaCO3 dissolves.
--------------------------------------------------------------------------
How to Measure a Particular Amount
Not everyone has a gram scale, and sometimes it may be more convenient to
prepare concentrated stock solutions and then add a portion to produce the
desired (diluted) concentration. On the other hand, precisely knowing the
resultant concentrations is not critical and therefore some standard
measuring devices (like fractional teaspoons) can be very useful to
approximate these small weights. Sometimes, the chemical comes in nicely
pre-packaged amounts, like Calcium tablets (Dietary supplement, pure
calcium carbonate), but generally teaspoon measures are sufficient. I have
discovered that for most chemicals, 1/4 teaspoon (t) = 1 to 2 grams. Here
are a few example concentrations resulting from 1/4 teaspoon of different
compounds and from calcium tablets.
------------------------------------------------------------------------------
Approximate
Compound Weight (g) Element Concentration (ppm)
per 1/4 tsp. or ion of 1/4 t in 50 gallons
----------------------------------------------------------------------
sodium nitrate 1.8 NO3- 7.0
sodium bicarbonate 1.3 HCO3- 5.1
ammonium nitrate 1 NH4+ 1.2
NO3- 4.1
potassium chloride 1.5 K+ 4.2
Potassium nitrate 1.4 K+ 2.9
NO3- 4.5
Magnesium sulfate 1.35 Mg++ 0.7
(hydrate) SO4-- 2.8
-------------------------------------------------------------------
Calcium carbonate Ca++ 3.2*
* (600 mg Calcium tablet) CO3-- 4.8*
Note: the carbonate is converted into bicarbonate after the CaCO3 dissolves.
-------------------------------------------------------------------
Molarity of Solutions.
Preparing a stock solution is another way to precisely provide the
amounts of material to create concentrations in the aquarium. Stock
solutions are often described in terms of molar concentration. This is
determined from the atomic weight. For example, potassium has an atomic
weight of 39.1 - one mole of potassium would weigh 39.1 grams and a 1 molar
solution of KCl is 39.1 g K per liter.
With solutions, milliliters (mL) are a standard unit of measurement. These
are found, for example, as the markings on the vials that come with some
aquarium test kits. (By the way, one mL is the same as one cc - a cubic
centimeter). Furthermore, the molarity of a solution is a standard way to
describe ionic concentration. A one molar solution of a molecule (or ion)
is a solution that contains the molecular (or ionic) weight, in grams,
* of that molecule (or ion) per liter of solution. Therefore, measurements
in milliliters of a molar solution is another convenient way to produce a
specific amount of material in milligrams. One milliliter of a one molar
solution contains one thousandth of the amount of material in a mole. For
example, one mL of a one molar solution of KCl contains 0.0391 grams or 39.1
milligrams of K.
Here is an example: Five mL of 1 molar KCl would be 0.005 liters, which
would contain 0.005 moles. Adding this KCl to 10 gallons of water (37.8
liters), we now have 0.005 moles K in 37.8 liters, or 0.000132 moles per
liter. Potassium has an atomic weight of 39.1, and so one mole of potassium
would weigh 39.1 grams. Multiplying the 0.000132 moles per liter times 39.1
grams per mole gives 0.00517 grams per liter or 5.17 milligrams K per liter
or 5.17 ppm. This procedure is an alternative to directly adding 0.195 g of
K (0.005 moles) or 0.375 g KCl (also 0.005 moles). In 50 gallons, 5
millimoles KCl produces approximately 1 ppm K.
Concentrations Resulting from Trace Element Powders.
A trace element mixture contains many different elements. The labels usually
indicate their composition in terms of their percentage by weight. For
example, PP Ltd trace element powder has 6 different nutrient trace elements
as presented below. Knowing their weight by percent allows a direct
calculation of the concentration resulting from adding a specific weight per
unit volume of water.
As an example, the following concentrations would result from 1 gram (and
0.25 grams) in 50 gallons of water:
---------------------------------------------------------
Percent Concentration (ppm)
Element by weight 1 g per 50 gal. 0.25 g per 50 gal.
---------------------------------------------------------
Fe 7 .37 0.1
Mg 2 .11 0.03
Zn 0.4 .02 0.005
Cu 0.1 .005 0.001
Bo 1.3 .07 0.02
Mb 0.06 .003 0.001
---------------------------------------------------------
Similar tables can be produced for different volumes, including stock
solutions.
If one wants to use the powder directly and not have to worry about storage
problems associated with the prepared solution, I discovered that the
measure that came with the Dupla test kits (e.g. iron kit) corresponds to ~
0.1 g of trace element powder. Therefore, 2 ½ measures in 50 gallons of
water will yield the desired Fe and other concentrations. A more precise
approach would utilize a stock solution and then a specific number of
milliliters of solute can be decanted for each application. Let's say that
one wants a solution of 5 milliliters to contain 0.25 g of trace element
powder. This means that one mL would contain 0.05 g and 1000 mL would need
50 g.
German, English and American Units for Hardness
There is a lot of confusion caused by many different units to measure
hardness. Sometimes hardness is expressed in terms of degrees. In the UK, 1
degree of hardness is equivalent to one grain of CaO per Imperial gallon of
water. In Germany, 1 deg (dH) is equivalent to 10 mg CaO per liter, while in
the U.S. water hardness is expressed in ppm of CaCO3. This is further
complicated by the distinction between general hardness (GH) and carbonate
hardness (KH). General hardness considers both permanent hardness caused by
all calcium and magnesium compounds including their sulfates and chlorides
and temporary or carbonate hardness based on the carbonates. Strictly
speaking, GH is always greater than or equal to KH. However, since KH is
measured as a bicarbonate, one can appear to have KH without any Calcium or
Magnesium in solution.
Here are some conversions:
1 degree of carbonate hardness (KH) = 17.9 ppm of carbonate
(measured as CaCO3)
1 degree of general hardness (GH) = 7.14 ppm Calcium
Or 17.9 ppm of CaCO3
Chemicals Used to Increase Carbonate Hardness (KH) and General Hardness (GH)
Carbonate and general hardness can be increased by using several chemicals
which are available in grocery stores, pharmacies and the aquarium shop.
These include Calcium Carbonate tablets (sold as a dietary supplement) and
sodium bicarbonate (baking soda).
One g of CaCO3 yields 5.3 ppm in 50 gallons,
so 3.4 g becomes 17.9 ppm or 1 KH.
CaCO3 tablets sold in the pharmacy as a dietary supplement are 1.5 grams;
thus 2 1/4 tablets are needed to raise one degree of KH. The tablets are
pure calcium carbonate and dissolve very easily. I put them in a one liter
bottle of water to create a CaCO3 suspension. When this chalky liquid is
poured into the water, it will take several hours before it will clear. This
is because it must react with CO2 to form the very soluble bicarbonate.
A solution of 17.9 mg/L of CaCO3 in water gives KH of 1. This
solution contains 0.179 mM Ca++, but does not contain any significant CO3--,
because this is converted to HCO3-, of which two are formed from each CO3--,
giving 0.358 mM HCO3-. We thus want 0.358 mM NaHCO3 in the solution. The
molecular weight of this is 84, so we want 30 mg/L sodium bicarbonate. In 50
U.S. gallons, this amounts to 5.68 g or a little more than 1 teaspoon (1.1 t).
-------------------------------------------
Amount to achieve
1 degree KH in 50
Compound Gallons of water
-------------------------------------------
Sodium bicarbonate 1.1 teaspoon
Calcium carbonate 2 1/4 tablets
-------------------------------------------
How to Increase Calcium Concentration and GH
Corresponding to the discussion of CO3, one g of CaCO3 yields 2.1 ppm of Ca
in 50 gallons of water. So, adding 2 Calcium tablets (3 g) will increase the
Ca concentration by 6.4 ppm. This is a little less than 1 degree of general
hardness. As with carbonate hardness 2 1/4 tablets are needed to get 1
degree GH. You will note that an increase of 1 degree of carbonate hardness
will also cause an increase of one degree of general hardness.
Concluding Remarks
Adding chemicals should be done with caution. Unless nutrient deficiencies
are known or specific target concentrations are desired, these actions are
not needed and could even be harmful. Monitoring water chemistry is
useful. This can be done by observing the behavior and appearance of the
plants and fish (i.e. looking for symptoms of deficience or toxicity) or by
performing chemical testing. There are many commonly available general (pH,
KH, GH) and chemically specific tests (e.g. Ca, CO3, NO3, NH4, N, Fe) which
will ensure a stable system. Some elements like Potassium (K), however, do
not have common home test kits, so increases beyond the uptake by plants and
fish does warrants some attention. There is also concern about relative
imbalance in concentrations because plants have the ability to consume more
chemical than they need and high concentrations of one element (e.g. Mg) can
block the uptake of other elements. Inhibition of nutrient uptake does not
appear to be a problem with other macro nutrients (N, P, K). Nitrogen can be
added in terms of Ammonium or Nitrate compounds. Although plants prefer the
former, the use of the latter is probably wiser, because of potential
ammonia toxicity to fishes at relatively low concentrations.
The directions for commercial nutrient preparations make assumptions about
fish load, amounts of fish food, plant density, growth rate and tap water
chemistry. Nevertheless, they do provide an indication of safe
concentrations, both in quantity and in their relative amounts. Aquarists
are advised to research their own water chemistry together with available
sources of information before they haphazardly start to dump stuff in the
tanks. One excellent way to reduce the chance of overdosing from routinely
adding chemicals, however, is to add them at the time of a water change and
at a rate less than the desired concentration. Although many chemicals are
partially or completely consumed by actively growing plants, it is still
theoretically possible that none may be used up between water changes.
Therefore, lacking precise information on chemical uptake, adding chemicals
should (1) generally accompany an X percent water change, (2) be done when
the replacement water is lacking that substance, and (3) at a rate equal to
X percent of the desired target increment. The latter is needed to ensure
that concentrations do not increase. For example, if the starting
concentration is 25 ppm and 5 ppm are added with each 20 percent water
change, then there will not be any increase in the final concentration.
Knowing the target concentration is not always easy to ascertain. The
range of safe concentrations is not always readily available. More
information is desired on the consumption rates in the aquarium and
desirable target concentration levels - both for individual chemicals and
for their combinations. Differences between hard and soft water situations
are also important.
Incremental concentrations of 1 ppm potassium and 0.5 ppm magnesium are
utilized in some commercial preparations for weekly dosing together with
biweekly water change. Potassium can probably be safely increased a few
fold. Nitrogen and phosphates are often omitted from commercial
preparations for aquarium plants, but aquarists have empirically determined
that 1-5 ppm NO3 are safe added amounts for nitrogen deficient tanks. As a
rough rule of thumb, these amounts would correspond to small quantities of
dry chemical: 1/4 tsp Potassium Chloride (Muriate of Potash) in 200 gallons
of water, 1/4 tsp Magnesium Sulfate hydrate (Epsom Salt) in 70 gallons of
water and 1/4 tsp of Sodium nitrate (Nitrate of Soda) in 70 gallons of
water. Alternatively, the K and NO3 can also be roughly achieved by 1/4 tsp
in 150 gallons of water. Assuming the replacement water does not have any
of these macro nutrients and there are no other suppliers of these
chemicals, then dosing with water changes ensures that long term
concentrations stay relatively low (0.5 to 2.5 ppm for Mg, 1-5 ppm for K and
5 to 25 ppm for NO3). With actively growing plants, the steady state
concentrations will invariably be much lower.
Acknowledgments
Thanks to Paul Sears for a general review and advice on carbonate
chemistry; and to Paul Krombholz for providing the example calculation of
ppm and molarity of solutions.
Neil Frank Aquatic Gardeners Association Raleigh, NC
The Aquatic Gardener - journal of the AGA - now in its seventh year!!