Hardness and Alkalinity - The Planted Tank Forum
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post #1 of 11 (permalink) Old 12-15-2006, 12:44 AM Thread Starter
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Hardness and Alkalinity

When I get my water tested I get something like 150 ppm for GH and KH. But I see people post numbers like 7 or 10 for their KH and GH on forums. How do you get these numbers from 150?


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post #2 of 11 (permalink) Old 12-15-2006, 02:02 AM
 
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Alkalinity numbers

Multiply by 10, 7 or 10 give you 70 and 100 ppm. Remember that 1 ppm= 1 milligram per liter (mg/l)

30 to 40 mg/l = soft water

100 to 120 mg/l = intermediate

120 and up = hard water
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post #3 of 11 (permalink) Old 12-15-2006, 02:04 AM Thread Starter
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Okay Thanks! Needed to know lol!


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post #4 of 11 (permalink) Old 12-15-2006, 03:30 AM
 
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Hardness and Alkalinity

For planted aquarium you should have:

Alkalinity (KH) = 30 to 45 mg/l (if you want a ph around 6.5 and 7)


General Hardness (GH) = 60 to 120 mg/l


To have a precise idea on GH, PH, KH go to:

warning: this is an advanced definition of those terms:

http://www.cichlid-forum.com/articles/gh_kh_ph.php

More:
Alkalinity
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post #5 of 11 (permalink) Old 12-15-2006, 06:07 AM
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Quote:
Originally Posted by Glouglou View Post
Multiply by 10, 7 or 10 give you 70 and 100 ppm...
No, this part is wrong.

GH and KH can be expressed in many different ways. The two most common ones are degrees and ppm (or mg/L).

There are conversions that you use to go from degrees of hardness to ppm and back. These same conversions are used for both GH and KH.

1 degree of hardness equals 17.86 ppm. As an example, how many ppm are in 4 degrees of hardness?
Answer: 4 degrees x 17.86 ppm per degree = 71.44 ppm.

1 ppm equals 0.056 degrees of hardness. As another example, how many degrees of hardness are in 120 ppm?
Answer 120 ppm x 0.056 degree per ppm = 6.72 degrees.

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Originally Posted by Glouglou View Post
...Remember that 1 ppm= 1 milligram per liter (mg/l)
This is true.
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post #6 of 11 (permalink) Old 12-15-2006, 04:29 PM Thread Starter
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Wow, lots of math! Thanks everyone!


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post #7 of 11 (permalink) Old 12-16-2006, 06:39 AM
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Naw it ain't either!

Do you know who Algebra was?

It was the mule on "The Little Rascals" that pulled the wagon around with the carrot on a pole in front of it's face.
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post #8 of 11 (permalink) Old 12-21-2006, 05:28 AM
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Quote:
Originally Posted by Glouglou
Multiply by 10, 7 or 10 give you 70 and 100 ppm...
Quote:
Originally Posted by Left C View Post
No, this part is wrong.
It is actually correct. See below.

Quote:
Originally Posted by Left C View Post
GH and KH can be expressed in many different ways. The two most common ones are degrees and ppm (or mg/L).
The other important part is to realize what standard you are referring to when reporting concentrations.

In Europe, and I presume Canada, degrees are converted to parts per million by 10 mg/L relative to the simple oxide of Ca or Mg (CaO). Here in the States we use the carbonate of calcium as the standard. They are equivalent:

10 x 10 mg CaO/L = 100 mg/L as CaO. Ca/Ca+O = 71.4% x 100 ppm = 71.4 ppm Ca2+

10 x 17.8 mg CaCO3/L = 178 mg/L as CaCO3. Ca/Ca+C+3(O) = 40% x 178 ppm = 71.4 ppm Ca2+

It's just that no one here bothers to specify, I think we all assume it is stateside.

It gets even funner with nitrate. The US EPA uses mg/L as "nitrate nitrogen" but some states (e.g., California) and Europe I believe report as "nitrate." So, the MCL of nitrate in US public water supplies is 10 ppm as determined by the EPA yet CA can provide water that is 40 ppm of nitrate. Because 10 ppm of EPA nitrate-N is actually 45 ppm nitrate. Are we having fun yet?
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post #9 of 11 (permalink) Old 12-21-2006, 03:15 PM
 
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TMI (too much info) !

This hobby is difficult enough without having to be a chemist or mathematician!

Just buy a test kit that reads in both degrees and ppm!
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post #10 of 11 (permalink) Old 12-21-2006, 06:23 PM
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Oh, come on now, make a little effort!

This is nothing more than one person saying they have a 10,000 aquarium, another saying it's a 10 and the third saying no it is 2.5. And they are all actually right. In this case, cc, liter, and gallon, respective.

The point is, saying one has "X ppm" of hardness is basically saying nothing; most of us (I do) assume one refers to CaCO3. For real precision and meaning, either stick with degrees or specify ppm of what.
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post #11 of 11 (permalink) Old 12-26-2006, 06:28 PM
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Originally Posted by Tsigoloeg View Post
It is actually correct. See below.



The other important part is to realize what standard you are referring to when reporting concentrations.

In Europe, and I presume Canada, degrees are converted to parts per million by 10 mg/L relative to the simple oxide of Ca or Mg (CaO). Here in the States we use the carbonate of calcium as the standard. They are equivalent:

10 x 10 mg CaO/L = 100 mg/L as CaO. Ca/Ca+O = 71.4% x 100 ppm = 71.4 ppm Ca2+

10 x 17.8 mg CaCO3/L = 178 mg/L as CaCO3. Ca/Ca+C+3(O) = 40% x 178 ppm = 71.4 ppm Ca2+
You're very right about going into the details. Hardness can be a little difficult to understand. I was just using the simple approah that I have used for hardness. I was basically using your formula in bold italics that was for CaCO3. James from Cali is in the US and I'm in the US; I didn't think that I needed to go into the other ones. I've been using the conversions from The Krib (Aquaria and Tropical Fish) and my Hagen test kit. I didn't feel that these were needed. I was just a litttle lazy.

These are my conversions from the Hagen Kit:
Multiply GH or KH(mg/L CaCo3) by X 0.056 = dH or/ou/o/gH
Multiply GH or KH(mg/L CaCo3) par X 0.07 = Clark H
Multiply GH or KH(mg/L CaCo3) por X 0.1 = fH
Multiply GH or KH(mg/L CaCo3) por X 1 = hardness
X 0.02 = mEq/L

Here's one of the many quotes from the krib. They used the same ones that I use. I believe that these are the ones most used. 1 degree of hardness equals 17.86 ppm. And 1 divided by 17.86 = 0.056. I put the formulas in bold italics and I quote it here. Water Hardness

"Water Hardness
by larry/creative.net (Larry Frank)
Date: Tue, 16 Dec 1997

After reading all the posts for hardness and alkalinity, I tried to go back through the aquarium literature that I have, and make some sense of all the different definitions, also tried to understand how all this affects CO2 addition. The following is what I came up with. My thanks to Dave (eworobe-at-cc.UManitoba.CA) for his help with understanding alkalinity. Any errors are mine not his.

Water Hardness
All fresh water sources contain calcium and magnesium in varying quantities. These are cations with a 2+ charge. They form salts with anions which have a negative charge. The most important of these are bicarbonate (HCO3- ; carbonate CO32- ; and sulfate SO42-.

General Hardness (GH) measures the cations (+ charge); for calcium and magnesium.

Carbonate Hardness (KH) Refers to only the bicarbonate, and carbonate anions(-charge); it does not measures the sulfates and other anions.

Carbonate Hardness is a confusing term because it does refer to hardness, but rather to the alkalinity (the ability of a solution to resist a pH change with an addition of an acid.) from the carbonates and bicarbonates. Other anions (such as hydroxide, borates, silicates, and phosphates) can contribute to the alkalinity. To be absolutely correct, you should NEVER use the term 'KH'; however, this is often refered to in aquarium literature. It should be noted that it is the bicarbonate/carbonate buffering system which provides the majority of the alkalinity in aquariums plant aquariums.

KH and GH are usually are close two each other, but the GH can be the same, higher or lower to the KH depending on the Cations and Anions in the sample. For example, a large amount of NaHCO3 would raise the (KH) and not effect the (GH). A large amount of MgSO4 would raise the (GH) and not the (KH).

Usually, in fresh water most of the cations are calcium and magnesium (In a 3:1 ratio) and most of the anions are carbonates. The levels for (GH) and (KH) will often be similar.

Units
It would make sense to measure the general hardness in # of ions/liter or molarity, but this is not used. The common units found in the literature are degrees of general hardness dGH (GH) from the German system or ppm Ca from CaCO3 . Carbonate hardness (KH) is a term which has nothing to d with hardness, rather it is the amount of carbonate or bicarbonate equivalents which effect the alklinity or acid buffering capacity. (KH) is equated to ppm CO3 from CaCO3

Converting from dGH and dKH to ppm CaCO3 can be accomplished by multiplying by 17.86 How the conversion factors were derived: (GH)
By definition, 1dGH = 10 mg/liter CaO

Atomic Weight Ca = 40, O = 16, CaO = 56

So 10 mg/liter CaO contains 40/56 *10 = 7.143 mg/liter of Ca

By definition ppm Ca is not for elemental calcium but for ppm CaCO3.


Atomic weight CaCO3 = 100

So 7.143 mg/liter of elemental Ca would be expressed as 100/40 * 7.143 = 17.8575 mg/liter(ppm)CaCO3.

1dGH = 17.86 ppm CaCO3 and 7.143 ppm Ca2+.

(KH)
1 dGH is defined as 10mg/lit CaO this can be related to ppm of CaCO3 as in above. Now the definition for dKH must have come from the amount of carbonate in 17.86 ppm CaCO3 which has nothing to do with GH wich is defined by CaO! Historically GH must have been defined first in terms of CaO; hardness in terms of ppm CaCO3 second, then KH third?

1dKH = 17.86 ppm CaCO3

From above; 1dKH = 17.8575 mg/liter CaCO3. 7.143 mg/liter of this is Ca, the rest ;(17.8575-7.143)= 10.7145mg/liter CO3

1dKH = 10.7145 ppm CO3

For bicarbonate:

CaCO3 forms Ca(HCO3)2 in water at pH less than 10.25 . (Two bicarbonates are formed from each carbonate ion):

CaCO3 + H20 + CO2 ---> Ca(HCO3)2

CO3 mw = 60
HCO3 mw = 61

Therefore 10.7145mg/liter CO3 from CaCO3 (each CO3 carbonate anion forms two HCO3 bicarbonate anions; 61/60*2 *10.7=21.8 mg/liter HCO3

Another way to calculate this is using molarity:

1dKH = 17.86 mg/liter CaCO3
mw CaCO3 = 100

17.86 mg/liter CaCO3 = .179 m Mole CaCO3

This will form 2* .179 m Mole = .358 m Mole
Multipling moles *mw will give mg:
0.358*61(mwHCO3) = 21.8 mg/liter HCO3

1dKH = 21.8 ppm HCO3

How to use these conversion factors:

If you have alkalinity in ppm or hardness in ppm divide by 17.86 to get degrees. If you want to raise the alkalinity by 1dKH using CaCO3: use 17.86 mg CaCO3
If you want to raise the alkalinity by 1dKH using NaHCO3:

mw Na = 23
mw HCO3= 61
mw NaHCO3= 84

1dKH= 21.8 ppm HCO3
21.8 *84/61=30 mg/liter of NaHCO3

using molarity:
0.358 mMoles * 84(mwNaHCO3) = 30 mg/liter of NaHCO3

CO2, pH And Alkalinity from Carbonates
CO2, pH and carbonates are all related by the following three equations:


1. CO2 + H20 <------> H2CO2 (Carbonic Acid)
2. H2CO2 <------> H+ + HCO3- (Bicarbonate)
3. HCO3- <------> H+ + CO32- (Carbonate)

Example of how increasing carbonates will either raise the pH or need counterbalancing CO2 added to maintain the pH level.
If NaHCO2 is added to aquarium water the additional carbonate ions will cause a shift to the left side of equation (2). This will form more carbonic acid extracting a H+ ion and thus raising the pH. The additional carbonic acid will drive equation (1) to the left creating CO2 which will dissapate out of solution bringing equalibrium at a higher pH. In order to maintain equalibrium at the original pH equations (1) and (2) must be shifted back t the right. This can be accomplished with the addition of more CO2 into the aquarium. (Equation (3) becomes important as pH approches 10.25)

These relationships are expressed in the familliar Chart with KH/pH and the amount of CO2 needed in solution to maintain a specific pH. The higher the amount of carbonates/bicarbonates in the aquarium, the more CO2 is needed to maintain a specific pH.


pH 6.0 6.2 6.4 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0
........._________________________________________ __________
KH
0.5 | 15 9.3 5.9 3.7 2.4 1.5 .93 .59 .37 .24 .15
1.0 | 30 18.6 11.8 7.4 4.7 3.0 1.7 1.2 .74 .47 .30
1.5 | 44 28 17.6 11.1 7.0 4.4 2.8 1.8 1.11 .70 .44
2.0 | 59 37 24 14.8 9.4 5.9 3.7 2.4 1.48 .94 .59
2.5 | 73 46 30 18.5 11.8 7.3 4.6 3.0 1.85 1.18 .73
3.0 | 87 56 35 22 14.0 8.7 5.6 3.5 2.2 1.40 .87
3.5 | 103 65 41 26 16.4 10.3 6.5 4.1 2.6 1.64 1.03
4.0 | 118 75 47 30 18.7 11.8 7.5 4.7 3.0 1.87 1.18
5.0 | 147 93 59 37 23 14.7 9.3 5.9 3.7 2.3 1.47
6.0 | 177 112 71 45 28 17.7 11.2 7.1 4.5 2.8 1.77
8.0 | 240 149 94 59 37 24 14.9 9.4 5.9 3.7 2.4
10. | 300 186 118 74 47 30 18.6 11.8 7.4 4.7 3.0
15. | 440 280 176 111 70 44 28 17.6 11.1 7.0 4.4
20. | 590 370 240 148 94 59 37 24 14.8 9.4 5.9

CO2 mg/liter
CO2 in excess of 40mg/liter is harmful to fish. Using this chart the alkalinity of the water from bicarbonates is balanced against a desired pH using CO2 to control the pH, making sure a unhealthy amount of CO2 is not called for.


--------------------------------------------------------------------------------

Hardness
by George Booth <booth/hpmtlgb1.lvld.hp.com>
Date: Wed, 17 Dec 1997
Great summary, Larry. I would only like to add the following for those who don't read between the lines:

The pH/KH/CO2 table is based solely on "carbonate hardness".
All KH test kits that I know of measure alkalinity, not true KH.
The CO2 value you get from the table will NOT be accurate if there are other sources of alkalinity in your water besides bicarbonate.
Even CO2 test kits are not accurate in the presence of other sources of alkalinity (phosphates, for sure).


Up to CO2 Plants The Krib This page was last updated 29 October 1998"
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