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Re: Hardness, Calcium, Magnesium

This goes to prove that a little knowledge can be a dangerous thing.

I guess from my previous and limited exposure to the oil business I was
thinking of
dolomite.  As I understand dolotimization of a limestone (CaCO3), ground
water containing Mg passes through CaCO3 and some Mg is exchanged for the
Ca.  Silly me, I assumed that would yield MgCO3.  This is particularly
important for those in the oil business - pronounced oal bidness in these
parts :) - as this greatly enhances the porosity and permeability of the
rock enabling it to hold a lot more oil and gas.  We all can drive cars,
heat homes (run aquarium pumps, lights, etc.) because lots of people have
found this rock in great abundance.  Considering this, you can understand my
surprise at the comments saying that MgCO3 does not exist or at least in any
great quantity.

Anyway, three things occurred to me that I should have thought of before my
posting.  First I'm an EE not a chemist or biologist.  If I had looked up
dolomite (that 'a little knowledge' thing again) I would have noticed that
dolomite is CaMg(CO3)2 not MgCO3.  I might then also have remembered that
this exchange takes place in the presence of a lot of water which should
lead one to conclude it is fairly insoluble.  Obviously this is not my area.
Which is why I joined this mail list and ask questions.  Not so bright ones
sometimes but some of us are destined to stumble in the dark until we see
the light.  Unfortunately, my time demands (work and family) do not permit
me to spend enormous amounts of time looking all this stuff up and filtering
through the old comments and other information on the web to decipher the
correct responses.  This is why I am so appreciative of all the input here
from those who do know and take the time to respond to all the redundant and
often near idiotic questions from those who don't.  Would it be too much to
say thanks again? A lot.

This however does not explain what is going on with the test which was the
reason for my question.  Perhaps expressed more clearly, what is going on in
the test?  From what I think I understand, Ca and Mg are the primary
constituents of general hardness and CaCO3 and Total hardness are the most
easily measured.  That permits one to extrapolate the concentration of Mg
from measurements of total hardness and calcium hardness.  Deriving the
percentage of Ca in CaCO3 is pretty straightforward from atomic mass but I
do not understand the how the numbers used in the calculation for Mg
concentration are derived?

For something more practical, my test kits finally came and I was able to
take some measurements last night and today.  All of these are LaMotte test

pH - <7.2    using octet comparator I would guess ~7.15
Alkalinity - 200 mg/l
Total Hardness - 108 mg/l
Ca Hardness - 60 mg/l    => Ca is 24 mg/l, Mg is 11.5 mg/l
CO2 - Not sure which value to use.  14-15 was first and very faint hint of
change to pink but did not turn clearly faint pink until 17 (19 by pH/KH
Nitrate - 6 ppm
Test says NO3 - N and to multiply by 4.4 for ppm NO3.  Does this mean 26.4
mg/l NO3?
Fe - ~ .05 +
Test kit says darker is higher but I'm not sure about this one - it looks
darker than the lowest color comparison but I do not see any pink (next
color sample in the comparator for .1).

Gerenal info:
10 gal tank (I know, bigger ones are on the way)
32 watt CF
80 F
Tank originally was started to be fish only.  Only discovered planted tanks
after I was 4-6 weeks into it.  Originally read a lot of stuff on George
Booth's website and have switched to Dupla stuff for water treatment
(Duplagan, Duplaplant 24, etc. for about 3 weeks now) once I could find it.
I think my water has been somewhat messed up before that and I'm trying to
do some water changes to get the other things I've tried out of the water
(old techniques from 15 years ago before I was trying for a planted tank,
LFS recommendations on planted tanks, etc.).  There is a bit of hair algae
that seemed to subside when I started the CO2 and got the pH down to 7.0 (I
think I know of one person who will probably say more CO2) and a little
standard green stuff on the glass and rocks.  This started when I began the
Dupla regimen but before CO2.

When I increase CO2 to the where the pH goes to 7.0, some of the fish look a
little funny - particularly the Otos and 2 Corys while the Tetras seem to be
happier (perhaps it's the pH).  Otos' breathing looks a little stressed or
they look a little lethargic and they have lost some color.  Corys seem to
have recovered.  I'm not sure if this is an oxygen problem or having the pH
move from upper 7's to near neutral over two days and they are acclimating
to the pH change.  When I started using CO2 I went pretty slow, gradually
increasing the bubble rate until the pH moved a little.  Not sure how long
it would take and did not want a bunch of dead fish.  With pH around
7.1-<7.2, plants are producing sufficient O2 to show bubbles on leaves and
some of the Gloss produces nice bubbles almost proportional to the bubble
rate of the CO2.

My inclination is to keep the pH around 6.9-7.0 and drop the KH closer to
4-6 so CO2 won't be too high.  When I last had fish the theory was that fish
health was improved and easier to maintain if the pH were neutral to
slightly acidic.  Is this still the accepted reasoning?  If I keep KH in the
11-12 range where it is now, a pH near neutral or slightly below would
require CO2 around 34-42 mg/l.  Will the fish get used to this or is this
asking for trouble?

I notice that in the Dupla and Dennerle books they recommend running CO2
around  35-40 mg/l but this seems much higher than what I perceive is the
general consensus among everyone here (around 15-25).  Dupla also runs NO3
around 25 mg/l, about 15-20 mg/l higher than I recall seeing most of those I
recognize here suggesting.

If the lower KH route is best, I would guess I need to add DI (LFS sells it)
or distilled water to get KH down to 5-6 range, dosing it with trace and
macro nutrients to keep the other things in the proper range.

Any suggestions would be greatly appreciated.

Charles Kuehnl

>From APD V4 #958
Jaime Johnson Wrote:

I wrote:

>> Not quite. There is no such compound as Magnesium carbonate
>> (MgCO3).

Roger, David and others replied:

>MgCO3 is the mineral magnesite.  It isn't especially common but it can
>be mined in large quantities.  That still has nothing to do with the
>hardness calculation.

Well, I was taught to never say NEVER, so my bad...Maybe what I
should've said is that's it's not all that common and comes in many
hydrated, hydroxy configurations. After checking a few sources, I found all
kinds of combos, like the ones David listed, but pure MgCO3 is still kind of

Roger Miller

Jamie    <"\\\>< Aquatic plants, water chemistry, and cichlids