# Does low KH cause issues with plant growth ?



## tubamanandy (4 Feb 2016)

I have very soft water and whilst I am fully aware of the dangers of low KH (low buffering/PH drops etc) what I am really concerned about is its effect on plant growth.

If my KH levels are generally 2-3, will this adversely affect plant growth or is the concern just lack of buffering ?


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## DRG93 (5 Feb 2016)

Nope. CO2, lights and ferts are the way forward. Don't worry about pH and KH. Although a good GH level can be beneficial by increasing the Calcium and Magnesium in the water.


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## ian_m (5 Feb 2016)

Low KH levels will cause issues with pH measurements and even more than usual, incorrect test kit results (including KH !!!). A cheap pH pen will need about 4-8KH to read correctly and an expensive one generally above 4KH.


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## tubamanandy (5 Feb 2016)

Thanks guys - I knew low PH is bad from a PH stability point of view but I'm glad is doesn't cause an plant growing issues


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## dw1305 (5 Feb 2016)

Hi all, 





tubamanandy said:


> low PH is bad from a PH stability point of view


 This is one of the problems with pH as  a measurement, it becomes less and less meaningful as you approach pure H2O. Soft, vegetated water will never have a stable pH, and this is true in nature,  as well as in the tank. 

I think about changes in pH in terms of changes in water chemistry, if you need large changes in water chemistry to cause small changes in pH then pH is biologically significant, if small changes in water chemistry cause large changes in pH, then it probably isn't. 

This is from Rocha, RRA.; Thomaz, SM.*; Carvalho, P. & Gomes, LC. (2007)
Modeling chlorophyll-α and dissolved oxygen concentration in tropical floodplain lakes (Paraná River, Brazil) _Brazilian Journal of Biology_ *69*:2. 






cheers Darrel


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## alto (5 Feb 2016)

tubamanandy said:


> I have very soft water





tubamanandy said:


> will this adversely affect plant growth


It can,  but with a KH of 2-3 you're fine


If you're interested in the actual science of the equilibrium between
_carbon dioxide (natural or added) & bicarbonate & carbonate_

this is really a nicely done treatise
*Carbonate equilibria in natural waters






*


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## Manuel Arias (18 Feb 2016)

Agreed. kH is key but not only for the pH. It is mainly due to the main form of inorganic carbon available in the water. Despite of some comments I read in the past, reality is aquatic plants are better adapted to intake HCO3 instead of CO2. This is still not totally true, but let's say that plants have a proton pump in place to do so: they are not really intaking HCO3- but instead they locally change pH to become HCO3- in CO2, which is absorbed as result of the exchange. Some plants are better fit for this purpose than others (e.g. _Hemianthus callitrichoides_, which a classic plant with very low efficiency intaking CO2 and then requiring high concentrations in water), so that is why kH can be an important factor for some plants.


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