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Old 01-30-2005, 03:38 PM   #1
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KH higher than GH???

I'm just wondering how my KH reading could be higher than my GH reading when KH is supposed to measure calcium carbonate hardness while GH measures both the calcium carbonate & magnesium salts??
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Old 01-30-2005, 06:02 PM   #2
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Not quite. GH measures Ca & Mg, & KH measures the carbonates (CO3 & HCO3).

If your water has only CaCO3, then the KH & GH would be equal. However, if your water has also NaHCO3, then you would have more carbonates than Ca/Mg, so KH is higher than GH. <Na is not measured by GH>

One reason for having NaHCO3 is using water softener - the water softener exchanges Ca/Mg for Na - in effect reducing GH & not KH.
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Old 01-30-2005, 08:00 PM   #3
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jsoong: I am trying to follow along -

So, water devoid of Ca and Mg would have a GH of zero, theoretically?

Would it be possible to have a KH of say, 50, and a GH of say 200? This example would be of hard water with little buffering capacity. Can that happen?

Just curious -
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Old 01-30-2005, 09:10 PM   #4
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Hmmm. . . weird thing is our water softner uses potassium instead of sodium because of the environmental damage the Na can cause. Plus I don't add much of that but use our RO instead because until just recently I had so much limestone in my tank that my hardness was really high.

You must be right about the sodium but I can't figure out where it is coming from. I have been doing cleaning & slow water additions of RO to bring the hardness under control. I do have vermiculite in my substrate which is from mica I believe but since its for planting that can't be my source of Na. I collected 1 piece of my driftwood from a freshwater area. I guess the other could theoretically be from the ocean but that is highly improbable considering how land locked we are. Not to mention the fact that my water was like that even before I added the questionable piece of driftwood.

Very mysterious??? I'm still confused????
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Old 01-30-2005, 09:31 PM   #5
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I just read through the GH and KH test manual. GH seems to be caused by the double charged cations like Mg++, Ca++, FE++, Zn++ . I bet that the K+ in your RO unit would not show up on a GH test, so maybe you dont have Na+? Funny thing is that I have never heard of potassium bicarbonate, but I have heard of sodium bicabronate. The fact that you are using a RO unit to lower hardness fits with what jsoong has said tho. I hate not totally understanding the tests I do!
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Old 01-30-2005, 11:49 PM   #6
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Quote:
Originally Posted by TomK2
Would it be possible to have a KH of say, 50, and a GH of say 200? This example would be of hard water with little buffering capacity. Can that happen? -
Strictly speaking Carbonate hardness (KH) should refer only to carbonate levels <obviously!>. So in theory, if you have water filled with CaPO4 (say), you will have high GH & no KH. However, the typical KH tests do not actually measure Carbonate levels. The test kit I have simple add acid until there is an acid crash, when the colour change. In that case, you are actually measuring buffering capacity. Some peolple prefer to call this test "total alkalinity" instead of KH. Total alkalinity will measure all the buffers (including the eg of CaPO4 above).

I suppose you could manipulate the water by just adding Ca/Mg without adding buffering capacity - eg Ca(OH)2 - but there would be no reason to do so.

Froggirl, the GH test will not measure K+ (as Tom had said), so if you have a water softener that exchange Ca/Mg with K, you get the same result as with a Na exchanger.

There are many ways to achieve the KH/GH levels you see. You can add NaHCO3 (baking soda), or even KHCO3. But you can also remove the Ca/Mg as in a water softener (using exchange resins).
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Old 01-31-2005, 12:11 AM   #7
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Thanks jsoong! This helps my understanding. Especially thinking of the KH as something other than hardness - alkalinity seems more appropriate. I could not understand how someone could have hard water but a nuetral or slightly acidic pH coming from the tap.
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Old 01-31-2005, 01:26 AM   #8
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Sorry about the double post.

I am not using the water directly from my water softner which softens with potassium chloride. What I have added to the tank is water that is run through a reverse osmosis system to remove all (most) ions. Our water is so bad here that sometimes there is warnings for citizens with high blood pressure not to drink the tap water so we have an RO system for drinking water. So unless we have a leaking RO membrane I'm not sure how the K+ would get through.

It is possible though so maybe this is my problem. Will a bit extra K+ hurt anything?? the difference in GH & KH is only like 1 or 2 degrees.
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Old 01-31-2005, 11:38 PM   #9
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IMO, healthy high KH is good for your tank, even a planted tank where you are shooting for a low pH. Good buffering capacity will mean a more stable tank, working against the natural acidification that will occur over time and can drastically (sometimes undesirably) lower pH.
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Old 02-01-2005, 12:59 AM   #10
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Hardnesses

It is very possible to have high KH and low GH or vice versa. Jsoog is absolutely right.

Its all very confusing!

In my tank, I have a KH of 0, and a GH of 5-7 degrees. I wish it were the reverse, I'd keep discus! I have to stabilize my KH using coral gravels, in a cannister filter (used as a KH generator). This in turn stabilizes my PH.

The KH's function in your tank is to lend or take ions as needed, to stablize the PH. Even a high KH can be exhausted over time if proper replenishment through water changes is not done.

There's LOTS of info out there on KH, GH and Hardness tests and understanding them. A google search will render more info than necessary!
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