🚀 go-pugleaf

_____________________________ test post________________________________

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 in recreational science is a set
of notes that may be useful to others who are trying to understand
but if there is sufficient interest
I will continu
e
 to post
 
my notes as I go along.  

SUMMARY

There are two main sections her
e. The first section summarizes the
essential quantitative facts neede
d 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 wa
s obtained by calling around to the
manufacturers and discussing the ch
emistry of their kits. Also several
people contributed via e-mail. I onl
y have experience with the LaMotte 
calcium kit so I may have missed 
s
ome information on the other kits.

LaMotte (and Hach) make test kits that
 measure total Calcium in solution 
and test kits that measure both Ca
lcium and total hardness. With the 
latter kits you can estimate magnesiu
m hardness too, but this is not too
useful for aquarists. For people that ha
ve Ca hardness test kits I describe
a delightful experiment that illustrate
s 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 eq
6




The terms "Carbonate Hardness" and "Ca
rbonate Alkalinity" are identical. 
They both refer to HCO3- and CO3-- co
ncentrations. Measurements of these
quantities are only indirectly relat
ed 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 f
actor to go from dKH to ppm CaCO3. 
Two points here. First, Thiel's ca
rbonate hardness test kit actually 
measures total alkalinity but the d
ifference between total alkalinity 
and carbonate hardness  is only abou
t 3%, so for us aquarists, there's 
no point in making an issue of it.  S
econd, according to Thiel, you can 
convert from his dKH figures t
o total alkalinity in ppm CaCO3 by 
multiplying the dKH figure by 18.9.
 I work through a detailed example 
calculation below. Moe and Thiel don't 
completely agree on their ppm CaCO3
to dKH conversion factors. Moe give
s the conversion factor as 17.9 or 
1/0.05 = 20, Thiel says 18.9.  The d
ifference may be related to the ~3%
difference between total and alkali
nity and carbonate alkalinity, but 
without further information I can't de
nd to Ca
anation of the "gotcha'
s
" involved 
in these conversions. 

Also, I'm still looking for more detaile
d data on the following test kits: 
Hach, Tetra, others?. If folks woul
d provide me with customer service 
telephone numbers and as much informat
ion about a particular kit as they 
have, I can try to follow through an
d get more detailed information on 
their kits. I might add that, I don't hav
e infinite funds to spend on phone 
bills, so if anyone else feels motivate
d 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 mill
igrams (mg) per liter (l) of fluid 
so  the units are (mg/l). One li
ter of water weighs almost exactly 
1 kg = 1000 grams . So concentrations ar
e often given in terms of (mg/kg). 
Now a milligram is  1/1000000 of a kg 
or 1 part per million ( 1 ppm). So 

f
or our purposes,  we have that