Re: water chem

[IDMiamiBob@aol.com]

In a message dated 7/6/1999 3:46:40 PM Mountain Daylight Time, 
megray1@pop.uky.edu writes:

> I think this topic has been beaten pretty well, like any dead horse should
>  be.  However, I am still having problems groking in fullness.  Could
>  someone please give their opinions on hardness, pH, and conductivity again?
>  I am using deionized water for water changes to lower my conductivity (it
>  is about 300 uS...I want about 1/10 that).  My hardness seems fine...1 deg
>  kH and 2 deg gH with the pH about 6.5 (I still want to lower it to about
>  6).  If the hardness is  what I am measuring why is conductivity so high?

General Hardness (GH) is a measure of ions with a +2 valence.  This includes 
Ca, Mg, St (strontium) and Ba (barium), and occasionally Fe, if it is in the 
correct valence form.  It is calculated by the test kits as though it were 
all Ca, which it isn't, but the majority of it is.  Carbonate hardness, aka 
alkalinity, aka KH, is the measure of ions which interact with H+ ions to 
neutralize them, thereby resisting a change in pH.  It is measured as CO3 
[-2valence], which again the vast majority of it is.

Conductivity is a measure of the waters ability to conduct electricity.  This 
conductivity is the result of all the ions in solution in your water, 
regardless of the ions' valences.  An ideal de-ionizer replaces all + valence 
ions with H+ ions, and all - valence ions with OH- ions.  Then the OH- and H+ 
ions attract one another and form H2O.

If you are using a budget-priced de-ionizer, you are replacing one Ca [+2] 
ion with two Na [+1] or K [+1] ions.  Twice as many ions means more 
conductivity than when you started.  It will also one replace CO3 [-2] ion 
with two Cl[-1] ions.  again, you've made conductivity higher.  Bummer, huh?

>  Also my deionized water reads 0 deg hardness, 0 uS 

Okay, great!  You've got the good de-ionizer.

>yet the pH is 8.5.  How
>  can this be?  

Because once you take out all the things which can cause the pH to swing one 
way or the other from neutral, the reading is really invalid.  Weird, I know, 
but true.

>I am adding pH down to get it to 6.5 and it seems to be
>  holding in the tank...ie not rebounding.  Thanks for any info

It isn't rebounding because your de-ionizer removed all those things that 
neutralize the acid, and cause the bounce-back.  Sounds to me like you are on 
the right track.  Be sure that you have the pHDown that specifies it has no 
phosphates, otherwise you will be posting again in a week wanting to know 
where all the algae is coming from.

You may want to add a little sodium bicarbonate (baking soda) to stabilize 
the pH.  Just a tad, mind you, or you will get that pH bounce back up in the 
bad range.  Also the more of it you add, the higher your conductivity will 
go.  Before deciding to add the bicarbonate, watch your pH closely for a 
while.  If you can avoid pH crashes, where it plunges really low, without it, 
then don't use it.

Bob Dixon


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