View Full Version : what does Kh and Gh mean?
thumper
11-28-2003, 7:27 PM
This is probably the stupidest question in the world, but I was curious anyway.
Slappy*McFish
11-28-2003, 9:18 PM
KH=carbonate hardness
GH=general hardness
Carbonate hardness is temporary hardness..it is the measure of bicarbonates/carbonates(calcium carbonate) in the water and has a direct impact on pH.
General hardness is the total measure of all dissolved minerals in the water. It is permanent hardness, and has no direct impact on pH.
GH test kits in the USA normally measure only calcium and magnesium in the water, not total dissolved minerals, which is TDS (total dissolved solids). TDS requires either a density measure or a conductivity or resistance measure.
MrGoodbytes
11-30-2003, 12:13 PM
Just wondering, but does the KH test measure carbonates (CO3^2-) and bicarbonates (HCO3^-)? I wasn't too sure about that.
Graeme
Slappy*McFish
11-30-2003, 12:22 PM
Yes, I'm believe most KH test kits measure both carbonate and bicarbonate ions.
Tim Bo
01-25-2004, 5:06 AM
I was reading through the archives and stumbled upon this thread. Please correct me if I'm wrong, but as far as I understand, most tests on the market don't test for genuine carbonate hardness, meaning they can't test specifically for HC03- and/or C03--, so when companies describe these test kits as KH testers they are technically incorrect; they test for alkalinity, not true KH (kh is a part of alkalinity). Generally, in freshwater tanks (with few phosphates or salts) bicarbonate is the main buffer...
Tim Bo - you are correct. KH is an alkalinity titration, not a direct measure of carbonate/bicarbonate. But in unadulterated water, the carbonate/bicarbonate system is the buffer/alkalinity/pH control of the water.
In tanks where folks have been adding supplments/buffers/"controllers"/"adjusters", GOK what is in the water. KH is not as infomative in adulterated water. But for those of us who do not add such products to our tanks, it is quite useful.