GH and KH - Should I care?

[Die Putzfrau]

Yes this is true, GH is not TDS, but GH influences KH which in turn influences PH. GH is derived mainly from the amount of cations Mg and Ca in water. KH is derived mainly from the amount of anions HCO3 and CO3 in the water. These cations and anions can form ionic bonds changing the buffering capacity of the water which affects the PH. So I guess GH doesn't directly affect the PH, but it still does in a way. This one website I looked at said that hard water always tends to have a higher PH.

 

[Kasakato]

Is there any way that you can test for TDS?

 

[Die Putzfrau]

Well technically no you can't since there are some very very small amounts of ions dissolved in water that really don't make a difference whether they're there or not. For example there might be 10 atoms of copper dissolved in a body of water. This exteremely small amount would have no effect on anything. It couldn't be picked up by any ordinary test that's available in stores. There's really no need to find the TDS in the first place.

 

[Watcher74]

GH is what determines the traditional meaning of hard water.

A water with high GH is "hard" to produce lather with soap.

KH is the amount of carbonates/bicarbonates in the water. According to my water report these are extremly high in our local source.

GH tests for Calcium and Magnesium. According to my water report these are extremely low in our local source.

Since these two tests, test for different things, how can they affect one another?

There are filtration methods that will drop your GH to nil and hardly affect KH one iota, which makes me doubt the assumption that these two types of hardness influence one another.

But if this is wrong, and someone can enlighten me, I will be very grateful and interested to know how I am misunderstanding.

 

[RTR]

Watcher - you are correct. GH is calcium and magnesium hardness, which has no effect on KH or pH. GH reflects whether or not it is "hard" to make a lather with soap. GH also affects the egg membranes of certain blackwater fish, making them hard to breed in higher GH water. Many water utilities treat the water to knock down Ca and Mg, to reduce scale build-up in pipes.

In most natural waters the GH and KH reflect the rock over and through with the surface or subterrainian water has traveled - if limestone is involved at all, both will be elevated and the pH likely will be high, but that does nor mean that GH affects the pH, only that the source of the GH also provided KH (carbonate and bicarbonate) in parallel with the Ca and Mg. There is a lot of limestone in the world, and carbonate/bicarbonate is the buffer system found in most natural waters. Only in places of torrential rains and their washing out of all soluble materials over geologic time do we see blackwater - as in the rainforests of the tropics, the costal rainforest of the Pacific Nortwest, and some restricted areas in the Applachian highlands

 

[Die Putzfrau]

Good question, after thinking for a while I realize that there's something that I must know first. Now does GH and KH measure the amount of Mg, Ca, CO3, and HCO3 all together? Or is it only the amount of these substances that remain by themselves, not bonded to anything else?
Regardless of what the answer is, I'm still sure that the amount of Mg and Ca does affect the buffering capacity.

 

[aquanewb]

Oh my goodness! It certainly seems like its a miricale that I was able to keep fish and plants alive for any amount of time when I was a kid. I have ordered GH and KH kits since I would like to have a plethera of plants at some point. Thanks for the info everyone. I see that there is a whole lot to know about a whole lot of stuff!

 

[RTR]

GH is a measure of the Ca++ and Mg++ ions in the water. Ions are just that, themselves, not associated with other things. KH is a measure of the alkalinity of the water, the ability of the water to resist pH change, and in unadulterated water is generally a good approximation of the HCO3- (bicrbonate ion) and the CO3-- (carbonate ion) in the water. If the water is adulterated by addition of commercial buffers, pH adjusters, etc by the hobbyist, or phosphates or orthophosphates at detectable levels by the water utility - then the KH measure will be less accurate to useless.

 

[Die Putzfrau]

Oh I see, thanks. But don't the Ca and Mg cations form ionic bonds with the HCO3 and CO3 anions in the water? If this happens, I don't know why it wouldn't, then that means that the GH influences the KH. Can someone clarify this for me?

 

[RTR]

These materials are fully ionized. If you dry the water out, as the concentration of the minerals in the water get higher from loss of water volume, they will fall out as carbonates and bicarbonates, among other salts.