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[APD] RE: Ca++/K+ in hard water... and K buildup

>> I have been following the threat about high K+ concentrations and Ca
>uptake and I wanted to add my story to the group.
>> Some time ago I stopped using RO water to reduce the hardness off my
>tapwater.  Currently I am using pure tapwater in my tank with a Gh +-20 
>and Kh +-15. 
>> I am also seeing distorted growth (which looks like a calcium deficiency)
>of some plants (echinodorus, ammania, hemianthus, ).  I assume it can't be
>a Ca deficiency because of the hardness of my tapwater.  I did dose a lot
>of potassium untill recently.  I followed the method advised by Tom Barr. 
>Last week I stopped adding the extra amount of K2SO4 after every water
>change on his advice on this list.  I have more than enough K because my
>KNO3 dosing is really high (almost no fish in the tank).

The only thing i can think of adding to Tom's great comments is to ask
about Pieter's KNO3 dosing and water change regime. K can build up in a
tank  under certain conditions. Otherwise folks wouldnt be telling us about
60-90ppm of K. Most people dont test for K, so it may not even be known. I
didnt know myself that I had 50ppm in one tank until I tested.

Build up WILL occur if you are adding more between water changes than your
plants consumed or that you take away (by dilution) from the water change.
Thats how it happens.  For example (extreme), if you are adding a tsp of
KNO3 daily and only changing 20% of the water monthly then the K can easily
increase. There are examples which are less extreme.  I can produce graphs
to demonstrate this.

Because KNO3 provides more potassium relative to its nitrogen than plants
need, this buildup is more likely to happen if you have few fish (ie.
little fish food to provide N). This is why I now use KNO3 in combination
with Ca2NO3. (Both infrequently in small amounts). But I have soft water,
so the Ca is an extra bonus.
Neil Frank
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Aquatic-Plants at actwin_com