# Which is more important kh or gh??



## fisherman (Apr 22, 2010)

Which one will shock fish?? just wondering cause i am kinda getting sick of doing a water change where i have to raise the stupid kh and gh.... almost everytime when i premix my water i would accidently raise the kh or the gh up by a tiny bit, then i would have to add more, water and then its not enough water, so i add more water, and then its too much water!!!!!! reason i ask which one is important, is cause many times i would have either the kh or gh added too much by 1 drop of the tester... sometimes its kh sometimes is gh... would 1 drop extra hurt the fish?


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## christhefish (Nov 8, 2010)

what kind of fish do you have?
it might not be important


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## neven (May 15, 2010)

in vancouver GH is more important since our water is practically RO water. I aim for 5 degrees in my community tanks

KH helps limit deadly ph swings from lack of maintenance or CO2 injection, aim for 2-3 degrees if you do not inject co2, 3-4 if you do.

Some species require high GH/KH to maintain optimal environments, but many species tank raised can live outside of parameters fine. Stability is the key. KH/GH swings (ie through water changes) cause more harm than PH swings.


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## teija (Sep 30, 2010)

Fisherman: It is the pH levels you really have to worry about with water changes. KH and GH do not have to be at a specific level before you put the water into the fish tank, but you want to make sure the pH is similar to avoid any shock. The KH and GH will level out with whatever the levels are in your tank already and shouldn't cause shock to your fish. What WILL cause shock is if there is a huge swing in pH (which is indirectly linked to your KH/GH anyway). I could be completely wrong but I think you are concentrating on balancing the wrong levels...


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## ncutler (Apr 26, 2010)

teija said:


> It is the pH levels you really have to worry about with water changes. KH and GH do not have to be at a specific level before you put the water into the fish tank, but you want to make sure the pH is similar to avoid any shock. The KH and GH will level out with whatever the levels are in your tank already and shouldn't cause shock to your fish. What WILL cause shock is if there is a huge swing in pH (which is indirectly linked to your KH/GH anyway). I could be completely wrong but I think you are concentrating on balancing the wrong levels...


From my understanding it's slightly different. It's the osmotic balance that needs to be maintained to avoid shock. This osmotic balance is acheived via consistency in total dissolved solids (TDS). if TDS changes, that causes osmotic shock which can kill a fish. Ph fluctuations can also harm a fish, but changes in TDS are much more severe.

GH measures magnesium and calcium levels in the water, so it can show some signs of what the TDS is (though is very limited and not a great way of testing TDS). It suggests that if GH remains constant, then one can feel that TDS might be staying somewhat constant.

I still lack a complete understanding of Ph versus TDS shock, but I do know from asking in many forums that Ph swings from C02 does not affect fish because of this osmotic balance (TDS).

To answer the OP: I myself would be more focussed on GH since KH would influence Ph and not TDS. But I'm interested to see what the general consensus is.


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