From: ahughes@arch386.hyperdesk.com (Arch Hughes)
Newsgroups: sci.aquaria,rec.aquaria,alt.aquaria
Subject: Test Kit Information and Others
Date: 5 Nov 92 21:35:28 GMT
Reply-To: Fernando Pineda <fernando@aplcomm.jhuapl.edu>
Followup-To: Fernando Pineda <fernando@aplcomm.jhuapl.edu>
Organization: HyperDesk Corporation

As per the request of Mr. Pineda, I am posting his study results.
Hopefully your follow-ups and replys will be directed to him because I
put Fernando's address in those fields (and because you'll be carefull
that you direct them his way)!

From: Fernando Pineda <fernando@aplcomm.jhuapl.edu>
_________________________________________________________________________
I noticed that my recent water chemistry post was corrupted. I'm not quite
sure what's happening. It appears that parts of my posts are being swallowed at
random by the network or by my system! Any advice from anyone with similar
strange experiences would be appreciated. I'm using TCP/Connect II under
multifinder on a Mac IIfx. In anycase, here are the notes including the calcium
buffering experiment, some simple calculations and the description the LaMotte
tesk kits.

----------------------------------------------------

My initial question about converting ppm CaCO3 to dKH resulted in an
explanation of the qualitative facts about hardness and alkalinity. My request
for the quantitative implications did not,however, meet with much success. So I
dusted off my old chemistry books, went to the library, did a few experiments,
and made some phone calls. The result of this little exercise is a set of notes
that may be useful to others who are trying to understand whatUs going on.

These notes are still incomplete, but if there is sufficient interest I will
continue to post my notes as I go along.

SUMMARY

There are two main sections here. The first section summarizes the essential
quantitative facts needed to understand and visualize some aspects of water
chemistry. The second section gives detailed information about test kits, i.e.
what they actually measure and how they do it (chemistry!). This information
was obtained by calling around to the manufacturers and discussing the
chemistry of their kits. Also several people contributed via e-mail. I only
have experience with the LaMotte calcium kit so I may have missed some
information on the other kits.

LaMotte (and Hach) make test kits that measure total Calcium in solution and
test kits that measure both Calcium and total hardness. With the latter kits
you can estimate magnesium hardness too, but this is not too useful for
aquarists. For people that have Ca hardness test kits I describe a delightful
experiment that illustrates how the buffering effect of CaCO3 maintains the
level of free Ca++ ions in solution. It demonstrates that that the time scale
of the CaCO3 equilibrium reaction is ~5 seconds or less.

The terms RCarbonate HardnessS and RCarbonate AlkalinityS are identical. They
both refer to HCO3- and CO3-- concentrations. Measurements of these quantities
are only indirectly related to the amount of calcium in the water through the
reaction CaCO3 + CO2 + H2O <=> Ca++ + 2[ HCO3-].

Thiel refers exclusively to dKH in his book (Advanced Reef Keeping). He gives
18.9 as the conversion factor to go from dKH to ppm CaCO3. Two points here.
First, ThielUs carbonate hardness test kit actually measures total alkalinity
but the difference between total alkalinity and carbonate hardness  is only
about 3%, so for us aquarists, thereUs no point in making an issue of it.
Second, according to Thiel, you can convert from his dKH figures to total
alkalinity in ppm CaCO3 by multiplying the dKH figure by 18.9. I work through a
detailed example calculation below. Moe and Thiel donUt completely agree on
their ppm CaCO3 to dKH conversion factors. Moe gives the conversion factor as
17.9 or 1/0.05 = 20, Thiel says 18.9.  The difference may be related to the ~3%
difference between total and alkalinity and carbonate alkalinity, but without
further information I canUt determine this. In any case, neither Moe nor Thiel
gives a satisfactory explanation of the RgotchaUsS involved in these
conversions.

Also, IUm still looking for more detailed data on the following test kits:
Hach, Tetra, others?. If folks would provide me with customer service telephone
numbers and as much information about a particular kit as they have, I can try
to follow through and get more detailed information on their kits. I might add
that, I donUt have infinite funds to spend on phone bills, so if anyone else
feels motivated to call and get information on a particular test kit, that
would help out considerably.


______________________________________________________________
NOTES
______________________________________________________________
DEFINITIONS , WEIGHTS AND MEASURES

Concentrations are often stated as milligrams (mg) per liter (l) of fluid so
the units are (mg/l). One liter of water weighs almost exactly 1 kg = 1000
grams . So concentrations are often given in terms of (mg/kg). Now a milligram
is  1/1000000 of a kg or 1 part per million ( 1 ppm). So for our purposes,  we
have that...

                                1 mg/l = 1 mg/kg = 1 ppm.

Concentrations of a chemical species are often given in units of moles per
liter. A mole is 6.022x10^23 molecules (a very large number).

When you see square brackets around the symbol for a chemical species
(e.g. [HCl] ) it refers to the concentration of that species. Usually
moles/liter.
---------------------------------------------------------------------------
ATOMIC AND MOLECULAR WEIGHTS

one atom of Hydrogen weighs 1.6725x10^-21 mg (mg = milligrams)

Atomic and molecular weights are given in multiples of the weight of hydrogen

element         symbol  atomic weight
hydrogen        H        1
Carbon          C        12
Oxygen          O        16
Calcium         Ca       40

Molecules           composition(symbol)     molecular weight

Water               H2O                     18
Carbon Dioxide      CO2                     44
Carbonic Acid     H2CO3                   62
Calcium Carbonate   CaCO3                   100
Carbonate           CO3                     60
Bicarbonate         HCO3                    61

Example calculation -- How much does a mole of Bicarbonate weight?

>From the table we find that a bicarbonate molecule weighs 61 times as much as
a hydrogen atom. A mole of bicarbonate molecules is 6.022x10^23 molecules.
and one atom of Hydrogen weighs 1.6725x10^-21 mg, thus a mole of Bicarbonate
weighs...

(6.022x10^23) x (61) x (1.6725x10^-21 mg) = 61,437 mg = 61.4 grams

Similarly, we can do a  mole of Calcium carbonate and discover that 1 mole
of CaCO3 weighs 100.7 grams.

------------------------------------------------------------------------
EQUIVALENT WEIGHT

Equivalent weight is a concept that comes up when dealing with acids.
One "equivalent weight" is the weight of a substance needed to provide ONE
mole of Hydrogen ions.

Examples:

Each ion of Bicarbonate (HCO3-) can only contribute one Hydrogen ion. So
one mole of  Bicarbonate is "equivalent" to one mole of H+. As we saw above,
one mole of Bicarbonate weighs 61.4 grams. So, we say the weight of one
equivalent of Bicarbonate is 61.4 grams.

What about carbonic acid? Well carbonic acid (H2CO3) contributes two H+ ions
per molecule. So it only takes 1/2 mole of carbonic acid to make a mole of H+
ions. So one weight of one equivalent of Carbonic acid is...

(6.022x10^23) x (62) x (1.6725x10^-21 mg) = 62,445 mg = 62.4 grams

1 equivalent of  H2CO3 = 1/2 * (weight of 1 mole  H2CO3) = 31.2 grams

We will mostly deal with milli-equivalent weights (meq) which is 1/1000 of
an equivalent weight. So we have

1 meq of HCO3  = 62.4 mg
1 meq of H2CO3 = 31.2  mg

Finally, we are ultimately interested in concentrations which are usually
stated as milligrams (mg) per liter (l) of fluid so the units are (mg/l).

(1 meq of HCO3)/l  = 62.4 mg/l of HCO3 = 62.4 ppm
(1 meq of H2CO3)/l = 31.2  mg/l of H2CO3 = 31.2 ppm


This same idea of equivalent weights gets used when dealing with Carbonate
hardness. In that case the one "equivalent weight" is the weight of CaCO3
needed to provide ONE mole of HCO3- or CO3--.

The point about CaCO3 equivalent weights is that they are not physical
concentrations of CaCO3. Instead it is the amount of CaCO3 you WOULD get IF you
combined the physical amount of HCO3- and CO3-- with enough Ca++ to use up all
the HCO3- and CO3--.
---------------------------------------------------------------------------
ALKALINITY

The following is taken from RChemical Oceanography, Millerno & Sohn, (1992).

"The total alkalinity of seawater is defined as the concentration of all the
bases that can accept H+ when a titration is made with HCl to the carbonic acid
endpoint."  (p. 283)

note: I assume that the carbonic acid endpoint refers to the point at which all
the carbonate and bicarbonate bases in the solution have been bound with H+ to
form carbonic acid.

DEFINITIONS

Total Alkalinity =  [HCO3-] + 2[CO3--] +        [B(OH)4-] + [SiO(OH)3-]
+ [MgOH+ ] + [ OH- ] + 2[ HPO4- ] + 3[PO4---]

Carbonate Alkalinity = [HCO3-] + 2[CO3--]

COMPOSITION  various bases contributing to total Alkalinity (at 25 degrees C?)
             in Seawater

                BASE       percent (by moles/liter )
                __________________
                HCO3-     89.8
                CO3--        6.7
                B(OH)4-    2.9
                SiO(OH)3-  0.2
                MgOH+      0.1
                OH-        0.1
                HPO4-      0.1
                PO4         ?

note: As you can see from the table, the difference between carbonate
alkalinity and total alkalinity is only about 3%. This difference is probably
much less  than the precision of the test kits commonly available to aquarists.

---------------------------------------------------------------------------

Illustrative experiment and calculation # 1:
                Free Ca++, bound Ca (CaCO3) and equivalent CaCO3, CaCO3 bufferin
g.
-----------

>From the atomic weight tables we see that 40% of the weight of CaCO3 is in Ca++

and the rest is in CO3--. Thus every 40 mg of Ca++ can form 100 mg of CaCO3.
That means that to get the CaCO3 equivalent of X mg of Ca++ you have to
multiply X by 2.5.

I bought a bottle of CaCO3 tablets and some distilled water (calcium carbonate
tablets available as Rcalcium supplementsS in the vitamin section of the local
drugstore, distilled water is usually available in the contact lens or water
section). The tablets I bought had 1500mg of CaCO3 each. I dissolved 1 tablet
in 0.1 liters of distilled water. I let my solution sit for a few days. Most of
the tablet wound up at the bottom of the beaker as a white powder.

I measured the Ca++ concentration using my LaMotte Ca test kit and got 64ppm
Ca++ (160ppm CaCO3 equivalent). So the 0.1 liter of water had 6.4 mg of Ca++ or
16 mg CaCO3 equivalent. This drives home the point that the CaCO3 equivalent is
not the same as CaCO3 actually added to the solution since I added 1500mg of
CaCO3.

Now, lets see the buffering effect of CaCO3 directly! You may want to read the
writeup below on the LaMotte Ca test kit. The test kit measures Ca++ directly.
In the process of measuring the Ca++ it removes all free Ca++ from the solution
by binding it to an indicator (calcon). The calcon turns red when bound to
Ca++. Next an EDTA solution is titrated into the solution which in turn strips
the Ca++ from the Calcon. The Calcon turns blue when the EDTA has removed all
the Ca from it and the titration is over.  Now think about the following
equilibrium equation

                 CaCO3 + CO2 + H2O <=> Ca++ + 2[ HCO3- ].

In the process of performing the titration, we have unbalanced the equilibrium
since the Ca++ has been removed from the right hand side. Physics demands that
some of the 1500mg of CaCO3 disassociate to rebalance the equation. So after
five seconds or so, your blue indicator turns red again! (WOW!)

Effectively, the calcon acts like a Ca++ sponge that is red when it is RwetS
and blue when it is squeezed Rdry.S The RspongeS is wrung out when you titrate
the EDTA. Each time you sop up all the Ca++ from the solution, the CaCO3 buffer
simply replaces it. This replacement takes less than 5 seconds, so it takes
about 5 seconds for the RspongeS to turn red after you have RwrungS it out. Try
it: keep adding EDTA until the solution turns blue, then wait a few seconds
until it turns red again. Add more EDTA until it turns blue, then wait a few
seconds until it turns red again, add more...Once you get this going it only
takes one drop to perform a blue/red cycle.

Sea water and aquarium water probably has very little CaCO3 floating around.
Most of it is bound up in the rocks, corals and sediment. So it is unlikely
that youUll see this effect when you test your aquarium water unless you happen
to have stirred up some sediment.

---------------------------------------------------------------------------

Illustrative calculation #2: Alkalinity -- converting from meq/l to ppm to dKH
-----------

Note: This is in here so you can see how the alkalinity and hardness fits
together quantitatively.

Moe states on p.34 of his Marine Reference that Sea Water has an ALKALINITY of
2.1 to 2.5 meq/l. HeUs not specific, but probably he means TOTAL alkalinity of
the species given above. We can make a simplifying assumptions to make this
calculation easy. If we assume the measurement was taken at a pH=8.2 and at
T=24 degrees C, then about 90% of the alkalinity is in the form of HCO3- (see
e.g. the composition table above). This means we can expect at most a 10% error
in our calculation if we assume that all the alkalinity is in the form of HCO3-
. We know that each meq of HCO3 is 1/1000 of a mole of HCO3-. So there must be
2.1x10^-3 moles of HCO3- in solution. To calculate the CaCO3 RequivalentS to
this much HCO3- we calculate the weight of CaCO3 if all the HCO3- were to bind
with Ca++. The reaction is

            CaCO3 + CO2 + H2O <=> Ca++ + 2[ HCO3- ].

We see  that each mole of HCO3- will produce half a mole of CaCO3. So we will
be left  with 1.05x10^-3 moles of CaCO3. This will weigh

(1.05x10^-3 moles)x(100.7 grams) = 105.7 mg of equivalent CaCO3.

or 105.7 ppm equivalent CaCO3.

Finally,  letUs convert this to dKH. The significance of the conversion factor
is not clear to me. Furthermore Moe and Theil disagree on the exact conversion
factor. Moe (p.36) says it is either 17.9 or ~1/0.05 (p.36) while Thiel (p.101)
says is is 18.9 . Lets take 18.9. This produces 105.7 ppm CaCO3/18.9 = 5.6dKH
which is in the right ball park. Similarly 2.5 meq/l of HCO3 translates into
6.65 dKH. This is a reasonable answer for sea water.
-----------
Note that the actual physical weight of HCO3- in solution can be calculated
from the alkalinity of 2.1 meq/l according to (2.1 meq/l HCO3) x 61.4
ppm/(meq/l) = 128.9 ppm of HCO3-.

---------------------------------------------------------------------------

REFERENCES

Advanced Reef Keeping 1, Albert J. Theil,Aardvark Press, Bridgeport CT,(1989)

The Marine Aquarium Reference, Martin A. Moe, Green Turtle Publications,
Plantation FL, (1989)

Chemical Oceanography, Frank J. Millero and Mary L. Sohn, CRC Press, Boca Raton
FL, (1992).
_______________________________________________________

SUMMARY OF TEST KIT INFORMATION
_______________________________________________________
KIT:       The LaMotte Test kit (Model CA-DR, Code:3609)

MEASURES:  This test kit measures Ca++ directly.

UNITS:

The reading is given in units of ppm Ca++ or in ppm (CaCO3 equivalent).

CHEMISTRY:

Reagent #1:  Sodium Hydroxide.

This boosts pH to 12-13 so titration will work and also precipitates
out of solution the Magnesium as magnesium oxide. This leaves only Ca
in solution (and trace amounts of other metals).

Reagent #2: Calcon

This is an indicator with a strong affinity for calcium. It bonds
to all the Ca++ in the solution. All the calcium (free Ca++ or
CaCO3) in the sample is eventually bound to the indicator. The
indicator is red when bound to Ca and blue when not bound to Calcium.

Reagent #3: EDTA a chelating agent

The EDTA has an even higher affinity to Ca than the
indicator. So as the EDTA is added to the solution,
it strips the Ca from the indicator in proportion to the amount
of EDTA added. When no Ca remains bound to the indicator it turns
blue. The amount of EDTA added to the solution up to this
point is proportional to the amount of Ca that was in solution.

REFERENCE:

LaMotte technical assistance 1-800-344-3100
---------------------------------------------------------------------------
KIT:       The LaMotte Test kit (Model <>?, Code:4824)

MEASURES:  This test kit measures Ca and (Mg++, Fe++ etc.) or just Ca++

UNITS:

The reading is given in units of ppm Ca++ or in ppm CaCO3  equivalent.

CHEMISTRY:

With this test kit you can measure either Ca hardness or total
hardness. Also, since 99% of total hardness in sea water consists of Ca
and Mg, you can estimate Mg hardness by doing both tests and
subtracting the Ca hardness from the total hardness)

Besides the reagents found in the Ca hardness kit (code: 3609) this
kit contains an additional indicator Eriochrome Black T which binds
to all divalent ions.

The Calcium test has the same chemistry as described above in the
Ca Hardness test kit. The chemistry for the total hardness test kit is
as follows:

Reagent #1:  Sodium Hydroxide.

This boosts pH to 10. So titration will work.

Reagent #2: Eriochrome Black T

This is an indicator with a strong affinity for all divalent ions( Ca++,
Mg++, Fe++, etc.)  All the divalent elements are eventually bound to
the indicator. The indicator is <color>? when bound to divalent ions
and <color>? when not bound the divalent ions.

Reagent #3: EDTA a chelating agent

The EDTA has an even higher affinity for the divalent ions
than the indicator. So as the EDTA is added to the solution,
it strips the divalent ions from the indicator in proportion to the
amount of EDTA added. When no divalent remains bound to the indicator
it turns <color>?. The amount of EDTA added to the solution up
to this point is proportional to the total amount of divalent elements
that were originally in the solution.

REFERENCE:

LaMotte technical assistance 1-800-344-3100
---------------------------------------------------------------------------


KIT:       Thiel Aqua-tech (Model: Carbonate Hardness, KH Test, Product No:1111)

MEASURES:

Customer service at Thiel claims that the test kit measures
Calcium Alkalinity [HCO3-, CO3--]. Their chemistry, however is a standard HCl
titration, therefore they are actually measuring TOTAL alkalinity. In any case,
at normal temperatures (25 C) this amounts to only a 3% error  (see ALKALINITY
).

UNITS: dKH  -- after applying a conversion factor that the kit supplies (2.8).

CHEMISTRY:

Instead of separate reagents the Thiel kit combines two reagents into a single
squeeze bottle.

Reagent #1:
A pH indicator dissolved in a dilute HCl solution (0.5% ?).
(Theil Aquatek would not reveal the particular reagent nor the exact dilution
of the HCl). The reagent is yellow-orange in the squeeze bottle. The indicator
is  yellow orange when in an acid and turns blue when the pH increases above
some value. I don't know the value but I guess that it is less than pH 6 or 7.

The HCl/indicator reagent is initially orange-yellow. When it is first added to
the sea-water solution it turns blue since the sea water is very basic compared
to the dilute HCl. As more reagent is added to the solution the HCl
disassociates into H+ and Cl-. The H+ binds with the bases until there are no
free bases left. At this point the H+ ions remain free, the solution becomes
acidic, and the pH drops dramatically. The indicator reverts to its yellow-
orange color. The amount of HCl added to the solution up to this point is
proportional to the total alkalinity.


REFERENCE:

Theil technical assistance 505-526-4000, (Al Bear)

REMARKS FROM A USER (Arch Hughs):

The reagent bottle comes "unpierced".  You have to poke a pin
through it.  It looks like (though I have not measured it) it would
hold about 5 cc of the reagent.  On occasion, the bottle won't
"behave" well and an air bubble forms at the tip while I'm making
drops and it becomes harder to count "good" drops.  Once in a long
while, I'll see a little "spray" (a few very tiny drops) come out
while I'm forming a "real" drop and I have to make a call about whether
to count that spray as a drop or not.  (Each drop only represents a
0.7 dKH step (computed as 2.8/4), so it's not very critical when your
result is in the mid teens.)

It (the test kit) comes with a nice 15 cc translucent plastic test
vial with red imprinted graduations, the single sheet instructions,
and all in a "zip lock" plastic bag.
My impression is that it doesn't provide anything close to the 50 tests
that the TFP catalog lists it as providing.  I'd say it provides more
like 10 or 15 tests.  Of course, mileage varies depending on your
KH....the higher the KH, the more reagent you use per test, and the
fewer tests you'll end up making per purchase.

"That Fish Place" item 055056, $12.95 each ($10.95 on sale now)
---------------------------------------------------------------------------
KIT:       Hach (Model ?, Code:?)

MEASURES:  Ca and total Hardness

UNITS:     ppm CaCO3, ppm Ca++

CHEMISTRY:


Reagents

REMARKS FROM A USER (K. Rogers)

It gives results as mg/l of CaCO3.  I only use the calcium part of the kit as
that's what I care about.  I did measure the total hardness of my tap
water when I first got it just to see what it was.  Total hardness is
meaningless to saltwater keepers.

REFERENCE:

Hach technical assistance telephone number
---------------------------------------------------------------------------
KIT:       Tetra (Model ?, Code:?)

MEASURES:

UNITS:

CHEMISTRY:


Reagents

REFERENCE:

Hach technical assistance ?

______________________________________________________________________________
Newsgroups: sci.aquaria