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Re: [APD] Lowering KH, Which Is Better: RO Unit or Strong Acid?
> Date: Sat, 25 Feb 2006 04:56:35 -0500
> From: cS
> Subject: [APD] Lowering KH, Which Is Better: RO Unit or Strong Acid?
> I hope that you ladies and gentlemen would be able to help me
> understand "WHY A STRONG ACID SUCH AS HCl, H2SO4, H2PO4, etc. SHOULD
> NOT BE USED TO LOWER KH" and that a RO unit does a much better job at
> it. I read many of the old APD posts and still am unable to
> Your assistance is much appreciated.
> - cS -
> The full discussion, if you're interested, can be found at APC when I
> raised the issue.
Don't even have to read either the discussion at APC or any of Frank's
responses to answer that one:
The simplest arguement for RO vs ACID boils down to mere ease- of- use.
When you use pure water (even not- so- pure) to dilute your start point, the
math and its outcome are far easier to predict and control. As with any
solution, concentration ratios are very straight- forward balances of the
amount of solute against the amount of solvent. These ratios are pretty much
a simple inverse relationship, as in:
If I want the concentration cut in half, I need twice the solvent.
If I want the concentration cut to 1/4 of its starting point, then I need 4
times the amount of solvent.
If I want 100 ppm, starting from 500 ppm, then I add pure water to mine
until I have 5 times the amount I started with... and the only thing I'm
adding is *water*.
On the other hand, if I use a strong mineral acid, I have to calculate
How strong is the acid? Is it 10%, 20%, reagent grade? How much of a
particular volume of this jug of acid will give me the number of hydrogen
ions I need to counteract the carbonate _and_ bicarbonate ions I wish to
remove? Come to think of it, how many carbonate / bicarbonate ions do I want
to remove? Can I perform equilibria calculations with any reasonable
precision? Can I resolve quadratic and log calculations? How accurately can
I measure the volume of acid I need? What's left in the water when I finish?
What happens to *me* if I spill the acid on myself or those around me? Do I
even have adequate protection from the acid fumes?
How masochistic are my tendencies? Do I want to take 10 seconds to solve a
problem and arrive at its solution by myself, or should I wait days for a
"committee solution". If I ask yet another committee, will they arrive at
the same consensus as the last one I asked? What is the esoteric value of
one committee's response against another's?...
David A. Youngker
jaafaman at comcast_net
...who realizes that this is just a singular response within _this_
committee ;-) ...
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