Gh/kh

[Squidward]

Hi All,

I have just done a KH & a GH test on my tank water using JBL test kits.

Both results came out the same = 11°.

Is this possible?
I thought that the GH was always higher than the KH?

Thanks
Squidward

 

[Bignose]

It is definitely possible. KH and GH measure different things. KH measures carbonate equivalents. That is, all the minerals that can act basic or acidic are compared to carbonate, and what is in the water is converted into an equivalent amount of carbonate. I.e. if there is 100 ppm of a mineral that reacts less than carbonate, say 55% as reactive as carbonate, that is set equivalent to 55 ppm of carbonate. If that was the only mineral in the water, that water would have a KH of 55 ppm. So, everything that is in the water is counted in this measurement.

GH is a measure of only the specific minerals it is to measure. Specifically only the metal divalent ions like calcium (Ca2+) or magnesium (Ma2+). Now, calcium and magnesium as basic, so they get measured in both test, but they aren't equal. I.e. 1 ppm of Ca2+ in GH is not equal to 1 ppm in KH -- again because the exact value of the KH is determined by how reactive it is compared to carbonate.

So, while in general GH is greater than KH, it is not necessary. Pure carbonate itself actually will not show up in a GH test, but will register on a KH test.