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Substrate research

Hi All,
It's been kinda slow this afternoon at work, so I started a little 
project I've been curious about for some time now. My tanks use a 
kitty litter/sand substrate and I've never had any complaints. First 
off, I don't move the big plants around to disturb anything serious. 
And, second, I don't have my 'mining cichlids' in those tanks, 
either. My cichlid tank is about to undergo big changes, I'm 
replacing the gravel bed with Fluorite. Being born with a very 
stubborn, analytical brain, I had to research. I was very curious to 
find what my substrates were made of, elementally. Since I work at 
a lab and do trace metal analysis, I knew it was only a matter of 
time before I got the best of myself. 

I did analysis on 3 samples: Fluorite, Wal-Mart Special Kitty litter, 
and soil from my garden. 1g of dry sample was pulverized by a 
mortal/pestal and digested according to Method 3050B EPA Soil 
method. *Disclaimer of method - This is not a total digestion. It is a 
very strong acid digestion that will dissolve almost all elements that 
could become "environmentally available". By design, elements 
bound in silicate structures are not normally dissolved by this 
procedure as they are not usually mobile in the environment.* This 
is still a VERY good representation of what is in the sample, as we 
use it daily for all kinds of solid samples. A Hydrofluoric acid 
digestion in more complicated, but more geologically correct, as it 
gets EVERY element in solution. I will do the HF digestion later to 
compare results. Should be quite interesting. Here's what I got:

Element            Soil (mg/kg)    Litter (mg/kg)   Fluorite (mg/kg)       

  Al                       5700              6000               6800
  As                        <                  8.1                 11.3
  Ba                       156               11.6                133 
  Be                       0.2                 0.5                 0.3
  Ca                      5800             14300               530
  Cd                       0.6                 2.4                  <
  Co                       2.6                 2.7                 3.4
  Cr                        10                  30                  6.2
  Cu                       73                 12.6                13.8
  Fe                     11500             14500              9610
  K                        433                2200               1700
  Mg                     1000               3760               1490  
  Mn                      136                47.5                85.5
  Na                       570                395                 444
  Ni                        4.1                 21.1                8.0
  Pb                       218 ?             9.3                  5.4
  V                         24.5              12.3                 8.8
  Zn                       248                70.5                33.5

Three things caught my eye. First, where did my garden get Pb 
from?? It's an old house and the garden in right against the wall, so 
maybe years of lead paint leaching from rainwater into my soil. I 
don't care, the veggies are delicious! Second, the As level in 
Fluorite. It's addressed in their website, it doesn't leach out and is 
no cause for concern.  And, third, does my cat know he is standing 
in Cd laced clay? I don't know where it came from, either, but 
again, it doesn't leach out. My water tests sooo clean from my 
tanks, and the only thing that ever shows is the things I add. I was 
real surprised to see how dynamic my litter was. It's loaded with all 
kinds of good stuff, plenty of Ca, Fe, K, and Mg. The soil looked 
good, too, except for the lead. The Fluorite was the least reactive of 
the three. It's hard as hell to grind up and just sits in the acid, 
where the other two fizz and bubble, mainly because of the Ca 
compounds and the organics in the soil. Small amounts of the litter 
and soil went into solution, but I think all of the Fluorite stayed in 
the beaker. It's like a crumbled brick sample. 
I've got to admit I'm impressed by them all. I would've bet any one 
of them would have lacked something important, but they're all 
comparatively good. I didn't test my gravel, probably something like 
950,000 mg/kg SiO2 ;-). I hope someone finds it all interesting. 
Now, it's time to wash and rinse 45lbs of Fluorite. 

Jamie Johnson
Greenwood, SC
jjohnson at davisfloyd_com
jjirons at greenwood_net  (home)