# GH, KH, significance towards plant growth and information



## HybridHerp (May 24, 2012)

So, I need a little run down on what ideal GH and KH levels would be for a planted tank, and the science behind what they mean and how they relate to each other.

I tested my GH and KH on my 75 but I'm not entirely sure what it means (I used an API test kit) but I'm thinking its long overdue for me to understand these two ferts.


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## Hoppy (Dec 24, 2005)

GH and KH are totally different. GH is the concentration of calcium and magnesium ions in the water. KH is the concentration of carbonate ions. Only when your magnesium and calcium are entirely from calcium carbonate and magnesium carbonate will the two be related. Calcium and magnesium are micro nutrients for the plants. Carbonate acts to raise the pH if you have any CO2 in the water, and you always do, from the atmospheric CO2. It also may buffer the pH a bit against acids in the water, except for carbonic acid.


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## plantbrain (Dec 15, 2003)

http://www.thekrib.com/Plants/CO2/hardness-larryfrank.html

http://www.thekrib.com/Plants/CO2/alkalinity.html


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## lauraleellbp (Feb 3, 2008)

http://www.plantedtank.net/forums/showthread.php?t=658826&highlight=kh


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## Diana (Jan 14, 2010)

GH is the more important from the fish point of view. 
I set the GH of the tank to suit the fish. 

Then I make the KH pretty close to the GH. 

If the fish comes from a black water system I will add peat moss, oak leaves or other things. 

Most aquarium plants do not much care what these values are, as long as they are not zero. 

All plants need the Ca and Mg that are measured when you test the GH. They use Ca and Mg in something pretty close to a ratio of 4 parts calcium to 1 part magnesium. The ratio in the water does not have to be exactly that, but somewhere in that neighborhood is good. 

A few plants can use the carbon from carbonates, but even these plants would prefer to get it from CO2.


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## VintonC (Aug 21, 2013)

Does the use of pressurized CO2 have any weight on what to set the KH level at?

Or does the KH level matter since the drop checker uses a standardized level for indication of CO2 level?


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## lauraleellbp (Feb 3, 2008)

I generally recommend people have at least a few degrees of kH to help stabilize/buffer a tank and also some slight side benefits of helping discourage calcium leaching from inverts, fish bones, etc.

CO2 is also acidic and will slowly break down kH. 

Someone doing regular water changes with average parameter tap water should not notice dramatic fluctuations in their kH levels.

If someone's tank or tap water is bottomed out on kH, it's easy and cheap to raise, lots of common products on the market. Baking soda is easy if all you need to address is kH.

I tend to recommend using something like Seachem Stability to reconstitute other trace minerals as well, for anyone using RO water for water changes.

Again, unless someone has extreme tap water parameters or has a goal of keeping/breeding some very specialized fish species, most hobbyists don't have to worry too much about their kH and gH and can work with what comes out of their tap and just do regular water changes to keep the tank parameters stable.


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## plantbrain (Dec 15, 2003)

VintonC said:


> Does the use of pressurized CO2 have any weight on what to set the KH level at?
> 
> 
> > No
> ...


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## plantbrain (Dec 15, 2003)

lauraleellbp said:


> I generally recommend people have at least a few degrees of kH to help stabilize/buffer a tank and also some slight side benefits of helping discourage calcium leaching from inverts, fish bones, etc.


My KH is 20 ppm, roughly 1 degree, I've found zero support for this over the years, I try and kill snails all day long, I can never rid the tank of them. 
It's rare unless someone uses pure RO to a KH less than 15-20 ppm. 



> CO2 is also acidic and will slowly break down kH.


This is wrong.

A tiny amount of the CO2 gas added converts 1/400th of the KH, but for all practical purposes, this assumed to have zero impact upon the KH by adding CO2. Anyone can add CO2 and then carefully measure their KH .....and verify this repeatedly on any planted tank using CO2 gas. Your KH will not change(at least due to adding CO2). 

The addition just changes what is there and then after degassing, the 1/400th of that KH is restored. It is not destroyed. Even if you lack all the alkalinity, 100% gone..........adding the same flow rate of CO2 gas will still yield pretty much the same thing, 399 vs 400 is a mere 0.25% difference, something we could not detect in a planted tank.You could not use the pH/Kh to measure CO2 this way (there's no HCO3), but, you could add a little bit of KH, then remove it, and keep the SAME CO2 gas flow rate and be able to assume safely that the ppm's of CO2 would be within 0.25% of the KH vs the no KH test samples. 

This KH, CO2 and acid base stuff gets most hobbyist. 



> Someone doing regular water changes with average parameter tap water should not notice dramatic fluctuations in their kH levels.
> 
> If someone's tank or tap water is bottomed out on kH, it's easy and cheap to raise, lots of common products on the market. Baking soda is easy if all you need to address is kH.
> 
> ...


This is factual.


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## lauraleellbp (Feb 3, 2008)

plantbrain said:


> A tiny amount of the CO2 gas added converts 1/400th of the KH, but for all practical purposes, this assumed to have zero impact upon the KH by adding CO2. Anyone can add CO2 and then carefully measure their KH .....and verify this repeatedly on any planted tank using CO2 gas. Your KH will not change(at least due to adding CO2).
> 
> The addition just changes what is there and then after degassing, the 1/400th of that KH is restored. It is not destroyed. Even if you lack all the alkalinity, 100% gone..........adding the same flow rate of CO2 gas will still yield pretty much the same thing, 399 vs 400 is a mere 0.25% difference, something we could not detect in a planted tank.You could not use the pH/Kh to measure CO2 this way (there's no HCO3), but, you could add a little bit of KH, then remove it, and keep the SAME CO2 gas flow rate and be able to assume safely that the ppm's of CO2 would be within 0.25% of the KH vs the no KH test samples.


I wasn't aware that the amount was so small. 

In practice, a planted tanker isn't going to be able to tell what part of kH drop over time is due to tannins or any of the other acids that tend to be produced in tanks, kH metabolism by plants, etc. 

*shrug* Regular water changes and avoiding extremes overall tends to be a strategy that helps a tank avoid a whole host of "evils;" however likely or unlikely they may be. Especially new hobbyists. Once someone has some experience under their belt, they have a better grasp on how far they can push what things and still be in the green.


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