pH, GH (General Hardness) and KH (Calcium Hardness).

murraycod

murraycod

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Sep 22, 2008
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Nthn Victoria, Australia
Hi Greg here,
I hope I'm going about this in the appropriate manner and am follow protocol.
I've spent quite a while reading various threads and especially the Freshwater Archives which i've found absolutely fascinating since the writers have been good enough to present their posts in layperson's terms.
However, as much as I've tried to resolve my questions through reading, I'm confused by a Freshwater Archive Thread in which RTR clarifies some general chemistry questions, but Famman writes about having GH 8, KH 5 & pH 8.2.
My pH is 7.4, which from my reading should be fine, but my 'Nutrafin' Test Kit, made by Hagen, gives me a KH 140mg/L & GH 120, with no clarification of GH being mg/L???
I have bore water, which I know has calcium and magnesium salts.
Can anyone suggest (a) why the difference between Famman's figures and mine (a different scale? ) and (b) should I attempt to buffer with peat or another product before I introduce corys, shrimp and plants?
My tank is 40 Gallon/160 Litres and has been cycling for several months.
Any light which people can shed on these points will be gratefully received.
Cheers,
Greg Murray
 
okay, so did you cycle with an ammonia source?

plants can usually be put in immediately(it depends on how hardy they are), I'm sorry I don't know mg/L nor the unit you are using, I use ppm... there are many ways people measure... PPM is for precise, while the unit you're using(I don't know what's it called) is used for less precision...
 
I haven't seen RTR on here in years...
Actually, ppm and mg/L are the same thing, at least in the small limit. mg/L are better to use if you want to consider any actual chemistry and convert to molar but I'm getting side-tracked. The German degrees of hardness convert to ~17ppm per degree, so I doubt your GH is 120dGH. It's most likely in ppm, like your KH kit. pH and KH/GH use different units. pH is the logarithm (the exponent you raise 10 to to get your number) of the molar concentration of hydrogen ions in an acidic solution. So as you may know, a pH of 2.0 is ten times more acidic than a pH of 3.0.
You are correct that your pH is fine. 7.4 is essentially neutral. In fact, it sounds like you have some pretty decent water. Not too hard or basic, but with good buffering capacity.

I always add my plants as soon as I can. They help with cycling by using up some of the nitrogenous compounds.
 
Thanks guys,
So Famman's GH 8 is 8 parts per million; I have 120. Should I be concerned?
And KH 5 compared with my 140 milligrams/litre.
Aha! Guys, I just read the EXTREMELY TINY writing on the card accompanying the hardness kit. (In 4 languages, too!)
"Multiply GH or KH mg/L CaCO3 by 0.056......"
120x0.056=6.72
140x0.056=7.84 Am I right in thinking then, that these are ppm figures, and that my water is fine, as you've suggested?
Sorry to be so slow on the uptake, but judging by the archives debate/thread, there'll be others who'll benefit from my embarassment/your patience and knowledge.
Cheers
Greg
 
I'm guessing that Famman's is in degrees, which works out to ~142.4ppm. You are right in concluding that your GH and KH are fine. The kit you have sounds like it measures in mg/L (or ppm), since the conversion factor they give you is 0.056, or ~1/17.8. Always remember that ppm is a lot bigger than degrees, since there are 17.8 mg/L in one degree of hardness.

Glad to help!:)
 
For a quick reference...

Alkalinity (KH):
1 mEq/L = 2.8 dKh = 50.04 ppm CaCO3
1dKh = 17.9 ppm CaCO3

Hardness (GH):
dH × 17.9 = ppm
ppm × 0.056 = dH


*the 17.9 is rounded up from 17.86
 
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Thanks All.
As with the Archive material I've read, I'll be re-reading these contributions regularly until I'm completely comfortable with them. All very interesting. My workshop is gradually becoming my dedicated aquaria/aquaponics/sustainable living site. Would anyone mind if I edit, print and laminate these technical notes for my own use?
Cheers Greg
 
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