water GH and KH
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water GH and KH

This is a discussion on water GH and KH within the Beginner Freshwater Aquarium forums, part of the Freshwater Fish and Aquariums category; --> What does it mean to have a low GH and a high KH?...

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Old 08-03-2010, 02:18 PM   #1
 
water GH and KH

What does it mean to have a low GH and a high KH?
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Old 08-04-2010, 12:02 AM   #2
 
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Hi,

Are you asking what the terms mean? Or are you asking about why they are different (GH low, KH high)? If the latter, can you provide the actual numbers?
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Old 08-04-2010, 07:33 AM   #3
 
low GH and high KH

my GH is about 0 and my KH is 240.
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Old 08-04-2010, 12:07 PM   #4
 
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I am not a chemist, so this is a very general response. GH is the general hardness which is basically determined by the amount of dissolved calcium and magnesium in the water. At zero you have very soft water with respect to general hardness. KH is the measure of carbonates (Karbon being the German for Carbon, hence the "K") which for our purposes is important for its buffering capacity with respect to pH. The higher the KH, the more buffering which means any attempts to change the pH will be very difficult; your KH is very high so long-term the pH in your aquarium should be quite stable. Fish are not affected by KH. They are very much affected by GH and pH, which is why in our fish profiles the "preferred range" for GH and pH are given for each species.

Usually the GH and KH are close, though not always as you clearly see in your case. For your aquarium purposes, your very soft water means soft acidic water fish will be right at home, though you might want to add some calcareous material to slightly increase the GH. Won't go more into this just now. What is your pH? Obviously that is also important for the fish.

Byron.
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Old 08-04-2010, 02:57 PM   #5
 
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Quote:
Originally Posted by Byron View Post
I am not a chemist, so this is a very general response. GH is the general hardness which is basically determined by the amount of dissolved calcium and magnesium in the water. At zero you have very soft water with respect to general hardness. KH is the measure of carbonates (Karbon being the German for Carbon, hence the "K") which for our purposes is important for its buffering capacity with respect to pH. The higher the KH, the more buffering which means any attempts to change the pH will be very difficult; your KH is very high so long-term the pH in your aquarium should be quite stable. Fish are not affected by KH. They are very much affected by GH and pH, which is why in our fish profiles the "preferred range" for GH and pH are given for each species.

Usually the GH and KH are close, though not always as you clearly see in your case. For your aquarium purposes, your very soft water means soft acidic water fish will be right at home, though you might want to add some calcareous material to slightly increase the GH. Won't go more into this just now. What is your pH? Obviously that is also important for the fish.

Byron.

Hi Byron,

You explained that very well...I somewhat already have an understanding of KH and GH but I could never explain it that well to make sense to anyone.

Comment/Question---Also you stated that GH and PH are really the concerns when having fish but for invertebrates you would want to monitor your KH because they do need the dissolved calcium & Mag for shell health...correct?

thanks,
-d
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Old 08-04-2010, 03:17 PM   #6
 
high GH and Low KH

My PH is 8.6. I don`t have any fish yet, i just finished fishless cycling the 150 gallon tank.Do i need to do something about the water?What fish would do better in that water? My other tank (55gal.thats up for one month) the GH is 0 the KH is120 and the PH is 6.5.I have lots of plants in there and a homemade CO2 thing.
I use water that has went through a water sofener and a carban whole house filter.and when i do a water change i use RO water.
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Old 08-04-2010, 06:30 PM   #7
 
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Quote:
Originally Posted by dfbiggs View Post
Hi Byron,

You explained that very well...I somewhat already have an understanding of KH and GH but I could never explain it that well to make sense to anyone.

Comment/Question---Also you stated that GH and PH are really the concerns when having fish but for invertebrates you would want to monitor your KH because they do need the dissolved calcium & Mag for shell health...correct?

thanks,
-d
As far as I understand it, it is the GH that is important, as this is the level of dissolved calcium (and magnesium) in the water; the KH is just the carbonates (carbon, CO2).
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Old 08-04-2010, 06:35 PM   #8
 
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Quote:
Originally Posted by bigmarj View Post
My PH is 8.6. I don`t have any fish yet, i just finished fishless cycling the 150 gallon tank.Do i need to do something about the water?What fish would do better in that water? My other tank (55gal.thats up for one month) the GH is 0 the KH is120 and the PH is 6.5.I have lots of plants in there and a homemade CO2 thing.
I use water that has went through a water sofener and a carban whole house filter.and when i do a water change i use RO water.

This is making mores sense now. You didn't mention a water softener previously, that explains the zero GH. And if you are also using RO water, your KH is being significantly diluted. Which is why the pH will be down to 6.5 which is good.

If you can provide that same water in the 150g, you could have a beautiful display of soft water fish. Any of the SA or SE Asian fish just about.

If you leave the pH at 8.6 you will need to add some hardness, maybe not use the softener. Fish that prefer higher pH generally need mineral (GH). That would mean rift lake cichlids, livebearers.
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Old 08-04-2010, 09:27 PM   #9
 
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So basically when you get your GH where it needs to be you should increase your KH enough to keep it stable..which I can't remember right now what number it is when it is stable..but that's how you get the pyramidal bond (I may have just made a word up) But by this I mean you get the balanced bond and no more headaches..
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Old 08-04-2010, 11:14 PM   #10
 
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Originally Posted by dfbiggs View Post
So basically when you get your GH where it needs to be you should increase your KH enough to keep it stable..which I can't remember right now what number it is when it is stable..but that's how you get the pyramidal bond (I may have just made a word up) But by this I mean you get the balanced bond and no more headaches..
To be honest, I have never bothered with KH. I have very soft water out of the tap (< 1 dGH and < 1 dKH) with a pH of 7.0-7.2 [they add soda ash I think it is to raise the pH which would otherwise be at or below 6 as it was until 2001, but it does not add hardness]. As I have mainly wild-caught SA and SE Asian fish I let some of the tanks just go, and the pH is around 5 as far as I can tell. On two tanks I like to have it around 6.2 so I have about half a cup of dolomite in a net bag in the top of the canister filter; this raises GH to around 2 dGH, and pH stays at 6.2 - 6.5 with the diurnal fluctuation common in planted tanks. I never measure the KH. This has worked for more than 10 years. I replace the dolomite when I remember, I have crushed coral in one of the tanks now because I can't find dolomite anywhere. So far (about 3 months) it has been working the same. I have been told that coral will not raise hardness like dolomite (latter has calcium and magnesium, coral is calcium) but so far it seems to work.
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