# water GH and KH



## bigmarj (Aug 3, 2010)

What does it mean to have a low GH and a high KH?


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## Byron (Mar 7, 2009)

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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## bigmarj (Aug 3, 2010)

*low GH and high KH*

my GH is about 0 and my KH is 240.


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## Byron (Mar 7, 2009)

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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## dfbiggs (May 19, 2010)

Byron said:


> 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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## bigmarj (Aug 3, 2010)

*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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## Byron (Mar 7, 2009)

dfbiggs said:


> 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.
> 
> ...


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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## Byron (Mar 7, 2009)

bigmarj said:


> 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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## dfbiggs (May 19, 2010)

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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## Byron (Mar 7, 2009)

dfbiggs said:


> 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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## dfbiggs (May 19, 2010)

Hmm that's interesting..I was going to ask you where you got the dolomite..maybe I can contact my old geology prof...I don't know if I can find it around here..after googling some pics I collected something that looks like it could be..i'll have to do the vinegar test. (I am a rock collector...:lol If I get a hold of some would you be interested?

Anyway if there's really no sense in monitoring KH I am wasting time..that is an annoying test..


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## Byron (Mar 7, 2009)

dfbiggs said:


> Hmm that's interesting..I was going to ask you where you got the dolomite..maybe I can contact my old geology prof...I don't know if I can find it around here..after googling some pics I collected something that looks like it could be..i'll have to do the vinegar test. (I am a rock collector...:lol If I get a hold of some would you be interested?
> 
> Anyway if there's really no sense in monitoring KH I am wasting time..that is an annoying test..


I haven't looked beyond the stores here for dolomite (i.e., online) but yes I would like some. Funny, back in the 1990's every store had it, it was a common white gravel for marine tanks, rift lake cichlids and livebearers because it (obviously) raises hardness and pH. I used it in the 1980's in my livebearer and rift lake setups. Now I can't find it anywhere (local stores).


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## dfbiggs (May 19, 2010)

Byron said:


> I haven't looked beyond the stores here for dolomite (i.e., online) but yes I would like some. Funny, back in the 1990's every store had it, it was a common white gravel for marine tanks, rift lake cichlids and livebearers because it (obviously) raises hardness and pH. I used it in the 1980's in my livebearer and rift lake setups. Now I can't find it anywhere (local stores).


 
Well I emailed my old prof. I'll see what she says. I'm pretty positive I have a head sized rock of dolomite but I am not willing to put it in my tank or break pieces off ...it is a memento and a piece of art to me. I was wondering if there is another use for it because it reminds me of kaolinite and I believe that is what they use for drywalling so that would be easy to get a hold of...

I wonder why they quit carrying it...maybe people got lazy and didn't want to worry about that montonus GH test..:lol:...you know this new generation...

Well I'll let you know when I find something out..

-D


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## Ulyaoth (Jan 9, 2010)

So KH isn't all that important? I finally went and did a whole range of tests on my tank about a week ago and found my KH to be low so I added some baking soda, partly because it's planted and according to some chart I found going by my KH and ph I would have low CO2 and I have some plants. My KH was about 40ppm(like 2.3dkh I think) and I added enough that it should about have doubled that and raised the ph some, which was at about 6.8. GH was around 100ppm, which is soft, right? I always thought I had hard water here but testing my pool right after filling it up this year it had just as low kh and GH about. Should it really matter for anything since I don't have cichlids? I have some platies too but they shoudl be alright, right?


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## Byron (Mar 7, 2009)

Ulyaoth said:


> So KH isn't all that important? I finally went and did a whole range of tests on my tank about a week ago and found my KH to be low so I added some baking soda, partly because it's planted and according to some chart I found going by my KH and ph I would have low CO2 and I have some plants. My KH was about 40ppm(like 2.3dkh I think) and I added enough that it should about have doubled that and raised the ph some, which was at about 6.8. GH was around 100ppm, which is soft, right? I always thought I had hard water here but testing my pool right after filling it up this year it had just as low kh and GH about. Should it really matter for anything since I don't have cichlids? I have some platies too but they shoudl be alright, right?


KH is important for its buffering capability, but there are safer and better ways to buffer than baking soda.

Sodium bicarbonate (baking soda) is frequently suggested as the way to raise KH. But in an article in the July 1996 TFH on maintaining tropical forest-adapted fishes in prepared water suitable to the fish, the authors point out that
...sodium bicarbonate has no effective buffer action and cannot stabilize pH in the face of additional acidic waste products. Also, one must not continually add sodium bicarbonate to adjust the pH because eventually the sodium ions present will reach intolerable levels. Adding a buffering solution that contains ions of calcium and magnesium of course produces undesirable hard water.​The authors of the above-cited article are Stanley Weitzman, Lisa Palmer, Naercio Menezes and John Burns, all top biologists; Dr. Weitzman is Emeritus Research Scientist now at the Smithsonian, and acknowledged as one of the most eminent scientists in this field.

The dolomite method I suggested previously is what the authors refer to as calcium and magnesium in the last sentence cited. But in very soft water, the rise in hardness is minimal, as I noted; in my tanks the tap water hardness of < 1 dGH becomes 1-2 dGH with about half a cup of dolomite (this is a 115g tank) and the pH is steady at 6.2-6.4 so dolomite works very well. So my resulting GH is no more than 35 ppm (2 dGH) and the dolomite has maintained this state with hardness and pH unchanged for years.

It depends upon the fish; soft acidic water fish that are wild-caught, which is the vast majority of fish in my tanks, come from waters with near zero or very slightly higher hardness, and acidic pH. You mentioned platys, which are livebearers; they will not do well in soft acidic water and should only be kept in basic harder water. If you have soft/acidic water out of the tap as I do, then using dolomite (if you can find it) or in that event crushed coral will work. The amount you need depends upon the tap water conditions.

Byron.


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