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[APD] Notes on the notion of high K+ causing Ca++ inhibition

Ghazanfar Ghori has peaked my interest in this topic about high K+
potentially causing inhibition of Ca++. 

He and quite a few others have observed their higher K+ levels causes some
issues with a few species of plants, namely Eustralis, Ammannia, Nesaea sp.
These are funny plants sometimes as it is. I was not staified with the
conclusions reached thus far. 
So faced with this and my on observations to the contrary, I've started to
look at high K+ potentially causing plant stress, growth inhibition or Ca
Most of the literature and studies I have seen and reviewed recently have
indicated that a more generalized salinity stress, rather than a specific
blockage of Ca++ uptake is the cause for inhibitory effects on plants. In a
sense, one could say that you are adding too much salt such as KCl or NaCl
A number of folks have searched inhibition K+/Ca++ and pulled up K+ gated
channel and ABA, second messenger etc. This is not relevant to the question
we are asking. 
Plant species vary in their ability to adapt to salt stress.
To test this, try adding some NaCl to the tank in close to the same
concentrations or less(say ??). Do not add any KCl or K2SO4 etc.
You should see similar effects I would suspect.
Adding K+ helps to reduce the Na stress affect.
Adding Ca++ in every reference I've seen that discusses it, says that this
reduces the high K+ affect quite readily.
So by adding more Ca++, you should have a reversal of the growth problems.  

If K+ is the issue, adding more Ca++ should take care of it.
Although I no longer have hard water with high Ca, I think a GH of 5 and
roughly 30ppm of Ca in the tap is not a high level by most standards.
I add 20ppm or so and have not had issues with these plants. 
So I'll stand behind my initial assumption that high K+ levels do NOT block
Ca++ uptake for the reason for problems with a few species of plants. 
A general assumption that all plants are blocked from high K+ levels is not
founded based on many past experiences with more robust species here on the
APD and my own observations.
That being said, you simply do not NEED that much K+ to begin with and if
it bugs you and you believe that high K+ concentrations do cause Ca++
blockage, add a little more Ca to your water, it'll never hurt to have
moderate GH's. 
A few public sites:  


You may want to look under salinity stress K+, etc rather than inhibition
by K+.

I have not found much evidence suggesting K+ at 50ppm, mg/l or less causes
issues. There are few specific cases where an aquatic plant was subjected
to high K+ levels and then noted Ca uptake, but it seems a general salinity
issue that can be rectified by having enough Ca++.
Folks with softer waters(less than 3-4) will want to add more Ca.
Tom Barr  

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