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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
> understand.
> Your assistance is much appreciated.
> - cS -
> The full discussion, if you're interested, can be found at APC when I
> raised the issue.
> www.aquaticplantcentral.com/forumapc/showthread.php?t=13828
> **********************************************

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 
_several_ items:
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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