# How to / KH Standards



## billionzz (Apr 9, 2005)

KH standards

Here is the information needed to make a KH standard. When I started using the drop checker method for measuring CO2 there was a lot of confusion as to the proper way to make a KH standard. After a lot of searching and asking questions I found the correct way to make a good KH standard.

I have made the KH standards with the following.


baking soda (sodium bicarbonate) 
sodium carbonate anhydrous
a lab certified Alkalinity Standard Solution as NA2CO3 in 10mL Ampules

How accurate you want the standard is up to you. I think the sodium bicarbonate and the sodium carbonate standards are very accurate if they are made right.

If you want a more accurate standard than that you could use the alkalinity standard solution. The reason for the increase in accuracy is because all that needs to be done is the dilution part, the weighing process is removed, which eliminates any errors from moisture in the sample or an inaccurate scale.

To make a KH standard using baking soda you would need the following.


distilled water 
baking soda (new and unopened would be best)
.01 gram scale (a calibration weight)
500 ml graduated cylinder
50 ml graduated cylinder

*1.* Measure 3000 ml of distilled water using the 500 ml graduated cylinder and put it in a clean container. The container could be an empty 1 gallon distilled water bottle. (I found it easier to use 3000 ml, instead of the often suggested 5000 ml because you can make your standard with 1 gallon of distilled water instead of having to have a larger container or multiple containers)

_To read the precise water level in the graduated cylinder._

-Place the cylinder on a flat surface.
-Make sure your eye is on a level plane with the of the meniscus. 
-The meniscus is the half-moon curve formed at the surface of liquid.
-Water should be read from the bottom of the meniscus

*2.* Weigh 3.60 grams of baking soda, add it to the 3000 ml of distilled water and mix well, this will make a 40 dKH / KH standard.

*3.* Pour 450 ml of distilled water into the 500 ml graduated cylinder.

*4. *Pour 50 ml of the 40 dKH standard into the 50 ml graduated cylinder

*5.* Pour the 50 ml of 40 dKH standard into the 500 ml graduated cylinder and mix well, this will give you 500 ml of a 4 dKH standard.

*6.* If you want a 5 dKH standard instead of a 4 dKH - change step 3 from 450 ml to 400 ml and you will end up with 450 ml of a 5 dKH standard.

A few addition items:

*1.* Don't heat your baking soda to dry it out or it will change from sodium bicarbonate into sodium carbonate. You could then end up with a mixture of sodium bicarbonate and sodium carbonate, this would change the sample weight needed because it takes less sodium carbonate to make the KH standard than sodium bicarbonate.

*2.* You can use sodium carbonate anhydrous instead of baking soda. When I found out that heating baking soda turns it to sodium carbonate I thought this might be a good alternative to using baking soda. I bought Lab grade sodium carbonate that is 99.95% pure, thinking it might make a more accurate standard. While in theory it should, I really can't say for sure that it does because when I follow the above instructions both the baking soda and sodium carbonate standards come out correct.

*3.* Not all of the calculators on the web are correct for calculating how much baking soda or sodium carbonate to use.

If you want to calculate your own weights here is the calculator to use.

'Reef Chemistry Calculator FV'

This calculator is correct, it was off when calculating sodium carbonate but Jose changed it in the last couple of weeks and now it's right.

This calculator rounds everything up because it was made for calculating 
aquarium water not small samples. To get precise weights just add some zero's to the sample size.
For example: if you wanted to know how much baking soda to add to 3 liters of water to get a standard that was 40 dkh the calculator would give you a weight of 3.6 grams to add. We want to be accurate to at least .01 grams so instead of putting in 3 liters of water you can put in 300 liters, the calculator will then give you a weight of 360 grams to add which you know would be 3.60 grams.

It has been said that there are a lot of assumptions built into these calculators but that's not correct statement for this calculator when calculating how much sodium bicarbonate or sodium carbonate to use for KH. This calculator will give you the same answer you would get if you calculated long hand, except that it rounds up the numbers (the solution for that is in the above paragraph).

Although there is one assumption in this calculator when using sodium carbonate, it assumes that the sodium carbonate is 100%. You will need to calculate the difference between your sodium carbonate and 100%
For example:
I purchased lab grade sodium carbonate anhydrous and it is 99.95% pure. After I calculate how much to use I have then multiply the answer given by the calculator by .5% and add that to the weight given by the calculator.

*4. *I have made these KH standards several times with sodium bicarbonate and sodium carbonate. When I follow the instructions listed above the standards has always came out right.

I have also made the KH standards using a lab certified Alkalinity Standard Solution as NA2CO3 in 10mL Ampules. As long as the accurate dilutions are done this should make the most accurate standard. This is what the EPA uses as an alkalinity standard when they are monitoring and assessing water quality.

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I hope this helps when others when they are making their KH standards and that they won't have to do all of the research I had to do just to get a good KH standard.

Bill


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## Patrice (Mar 8, 2006)

Thank you Bill. this help me lot. 
I will try again with sodium bicarbonate. I will use mutch beter tools next time. (my ballance mesure only up to 0.1 and I was using a cooking mesuring cup).
I also want to give a try to the Alkalinity Standard Solution. where can you buy solution like this?

regards,

Patrice


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## billionzz (Apr 9, 2005)

>>> I also want to give a try to the Alkalinity Standard Solution. where can you buy solution like this?
regards,
Patrice<<<

Hi Patrice,

I have some standards listed on the "for sale or trade" forum here at APC and they are listed on Aqua Bid under 'test kits"

Bill


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## furballi (Feb 2, 2007)

Your local water company should be able to provide a very accurate reading of KH expressed in ppm. Divide by 17.8 if you want the result in the traditional German buffering capacity unit.


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## billionzz (Apr 9, 2005)

The main use for the KH Standard is to use it in a drop checker to monitor the CO2 in your aquarium.

I don't know how other water companys are but I live on the bay in Texas and our water is a mix of 10% ground water and they pipe in the other 90 % as surface water. This causes a lot of variation in my water I could have 5 dKH one day and 11 dKH the next day.

Bill


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## hoppycalif (Apr 7, 2005)

Sacramento's water supply can come from river water - low KH/GH and/or well water - high KH/GH. I have measured hardness from about 1 degree to about 6 degrees for our water. The water company water quality report just lists ranges for all of the parameters, and the ranges are pretty wide.


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## thefishmanlives (Feb 15, 2008)

I dont have graduated cylinders, where can i buy cheap ones or something else that will work to measure what i need to make this solution?


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## hoppycalif (Apr 7, 2005)

thefishmanlives said:


> I dont have graduated cylinders, where can i buy cheap ones or something else that will work to measure what i need to make this solution?


Ebay has lots of listings for various lab glassware. I got mine that way. I purchased a 1000 ml (1 liter) flask, and a 100 ml graduated cylinder. But, there is a wide variety of such glassware available.


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## tropism (Jul 21, 2006)

thefishmanlives said:


> I dont have graduated cylinders, where can i buy cheap ones or something else that will work to measure what i need to make this solution?


In a pinch, you *could* just use a calibrated scale. 1 ml of distilled water has a mass of 1 gram. That means that you could measure out 3000 grams of distilled water, and then add 3.60 grams of baking soda to it (Steps 1 & 2) to get a 40 dKH standard. The change to the volume of water after the addition of the baking soda is negligible, and the new density for the 40 dKH solution is approximately (3000g + 3.60g) / 3000 ml = 1.0012 g/ml. So to get the 50 ml of 40 dKH standard (for Steps 4,5), you could weigh out 50.06 grams of it.

I wouldn't really recommend this though... It could be quite a pain get 3000 ml of water by weighing it because you might have to measure multiple smaller amounts. For example, the most common scales accurate to 0.01 g only weigh a max of 50-100 g at a time (less when you consider the weight of the container the water's in). It could also be more prone to error, depending on how many separate measurements you have to make to get the 3000 ml. If you have a scale that can weigh 1000 g or more at once but is still accurate to 0.1g, that would work to measure the larger amounts of water, but you'd still need a scale accurate to 0.01g to measure the baking soda.


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## tropism (Jul 21, 2006)

billionzz said:


> *1.* Measure 3000 ml of distilled water using the 500 ml graduated cylinder and put it in a clean container. The container could be an empty 1 gallon distilled water bottle. (I found it easier to use 3000 ml, instead of the often suggested 5000 ml because you can make your standard with 1 gallon of distilled water instead of having to have a larger container or multiple containers)
> 
> _To read the precise water level in the graduated cylinder._
> 
> ...


I was looking at this thread last night to make up some KH solutions and I think the instructions for making a 5 dKH standard are off. Shouldn't adding 400 ml of distilled water to 50 ml of 40 dKH standard give you a 4.44 (not 5) dKH solution? (Please correct me if I'm wrong on any of this)
*
for the 4 dKH standard:*
take 50 ml of 40 dKH solution --> 50 ml * 40 dKH = 2000 ml*dKH
add 450 ml distilled water to make 500 ml --> 2000 ml*dKH / 500 ml = 4 dKH

*for a 4.5 dKH solution:*
take 50 ml of 40 dKH solution
add 394 ml distilled water to make 444 ml --> 2000 ml*dKH / 444 ml = 4.5 dKH

*for a 5 dKH standard:*
take 50 ml of 40 dKH solution
add 350 ml of distilled water to make 400 ml --> 2000 ml*dKH / 400 ml = 5 dKH

--

For those not so great with math... If you want to know the amount of distilled water to add to a 'KH standard' to get a final solution with a (lower) specific dKH:
A = volume (ml) to use of KH standard
B = dKH value of the KH standard you're using
KH = desired KH
V = total volume (ml) of final solution
DW = amount of distilled water to add

(A*B / KH) - A = V
V - A = DW​
examples:
if you start with 50 ml of a 40 dKH standard and want a final solution of 4.5 dKH:
(50 ml * 40 dKH / 4.5 dKH) = 444 ml final volume
444 ml - 50 ml => add 394 ml of distilled water to the 50 ml you started with

if you start with 100 ml of a 5 dKH standard and want a final solution of 4 dKH:
(100 ml * 5 dKH / 4 dKH) = 125 ml final volume
125 ml - 100 ml => add 25 ml of distilled water to the 100 ml you started with


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