# How to calibrate KH test kit



## mstolpner (May 11, 2005)

Hi,

I am using ph controller so proper KH reading is important for me. I am reading 60ppm from my Nutrafin test kit and 5 dKH or ~80-90ppm from my Aquarium Pharm test kit. Can you please suggest how to calibrate KH test kit?

Thanks,
Mikhail


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## mstolpner (May 11, 2005)

I just found an answer.  http://www.cnykoi.com/calculators/calckh.asp


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## jerseyjay (Jan 25, 2004)

That link looks good but just in case you want to try this approach:

Double the sample water amount in your testing tube and divide result by 2. This was always more accurate for me.


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## TWood (Dec 9, 2004)

Here's a calculator set up for smaller bodies of water:

http://dataguru.org/misc/aquarium/calKH.asp


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## mstolpner (May 11, 2005)

*Graduating test kits*

I tried calibrating both kits and I found the same problem on both of them - they do not provide reliable results across the scale. I think that plantbrain mentioned that problem many times. For example, for 40 ppm kh solution, a test kit showed about 40 ppm, but for 80 ppm it showed only 60ppm. So I decided to graduate it using the following method. I beleive it can be used for many titration test kits. I am not very strong at chemistry, so may be someone can validate this method.

1. prepare a reference kh solution (100ppm): 1.40g of soda for 10l of distilled water
2. add few ml of distilled water to a test-tube. this amount is not important.
3. add 1 drop of kh titration solution from the test kit assuming that your drop is 0.05ml (and assuming your test kit requires 5ml water to test). it should get its final color according to the kit manual.
4. add and count drops of the reference solution until the solution changes its color. each drop will add 1ppm to the solution being tested. Put a graduation record somewhere (probably on the test kit bottle): 1drop - 10ppm(or whatever # of drops you had to use to change the color instead of 10ppm).
5. repeat steps 3 and 4 and add next record: 2drops - 20ppm (or whatever # of drops you had to use to change the color instead of 20ppm).
6. Repeat steps 3 and 4 as many times as you need to complete your graduation table.

Now you can simply count # of drops of titration solution as per kit manual but read the kh value from the graduation records. Instead of ppm you can graduate it with dKH if you want to. One who needs more accurate results can also go further with this method:

1. add drops of titration solution to water being tested until it changes its color. save the number of drops as the first number.
2. add drops of reference solution until the solution changes its color back. save this number as second number.
3. refer to graduation table and read ppm for the first number of drops.
4. subtract second number of drops from the ppm number. the result is kh value with 1-2ppm precision.

Mikhail


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