# Unit of Measurement for GH and KH



## Iwagumist (Jan 4, 2016)

I use the API liquid test kit to measure my KH and GH, and I am really confused :confused1:. In the back of the instructions is a conversion chart for the test readings, and it has two different units of measurement: dKH and ppm. So, does dKH measure KH and GH or just KH? Also what degree is considered hard and what soft in a planted tank? My KH is reading about 8 dKH (143.2 ppm) and the GH is 9 dKH (if you can use that unit for GH) or 161.1 ppm. Is that really hard? Any advice is welcome :grin2:!


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## Audionut (Apr 24, 2015)

Degrees and ppm is exactly the same as metric and imperial, they both measure exactly the same thing.

KH is KH, and GH is GH. Doesn't matter what scale they're being measured in, degrees or ppm. One degree of general hardness (dGH) equals 17.848 ppm of general hardness (GH). One degree of karbonate hardness (dKH) equals 17.848 ppm of karbonate hardness (KH).

https://en.wikipedia.org/wiki/Hard_water#Hard.2Fsoft_classification
Note that this applies only to the GH measurement of the water.


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## Hoppy (Dec 24, 2005)

If you measure your KH and GH with a kit that reads one degree of hardness per drop of reagent, the real relationship between 9 dKH and ppm is 180 ppm, or even 200 ppm. When you measure something and read out in one digit, only one digit is useful when you convert that reading to something else. For sure you can't reasonably use 17.848 as the conversion factor.


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## Iwagumist (Jan 4, 2016)

I just read back over my question and I don't think my question was very clear... What I am TRYING :grin2: to ask is this: can GH be measured by dKH, or can it only be measured in dGH? Or is there even a difference? The API test uses a one drop to one degree of hardness ratio, but only has dKH marked down on the chart, no section for dGH. So does the one drop to one degree ratio only work for KH or does it work for GH as well? Hope this is making sense... here is a pic of the chart:


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## Audionut (Apr 24, 2015)

Hoppy said:


> For sure you can't reasonably use 17.848 as the conversion factor.


For sure you can reasonably use that figure as the conversion factor, because that is what it is. Without doubt. To suggest otherwise is to breed uncertainty.

If the test kit has an accuracy of +/- 10 ppm, that is another issue entirely.


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## Hoppy (Dec 24, 2005)

The circumference of a 1 inch diameter circle is 3.14159265359, not 3.14159265357:laugh2: Sorry, I'm an engineer.


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