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Role of potassium in and out of water

Not so long ago, I asked about an optimum ratio of nutrients in our tanks. I'll see if I can track it down. But the outcome of the discussion was that there possibly wasn't an optimum ratio.
The issue gets much more complicated when there's any clay in the substrate. A few basic facts about clay minerals:
(1) Clays possess a cation exchange capacity. Let's always keep in mind that a proton (H+) is also a cation, and can occupy an exchange site.
(2) There are many kinds of clay minerals originating from many deposits. Each and every of them comes with some amount of cations bound, and each has its own affinity for every cation.
(3) This affinity interacts with outer environment. Par example, such a clay may accept more protons in acidic water while releasing some other(s), again in respect to their abundance.
Now, plants - not even species, but often even individual plants - differ in their dependence on nutrients taken up from substrate or water column. Obviously, if there are substances with adsorption capacity (a broader term than CEC) within the substrate, the ratios among elements are different in the substrate and the water column.
I've been studying nutrient ratios for quite a while. To minimize the influence of substrate (and its compounds with adsorption abilities) I stick to clean (acid washed) silica sand. Still, I can't avoid some detritus accumulation in the sand. (I don't vacuum it not to disturb microbes living there.) Detritus too has significant adsorption ability.
In sum: If we all kept our tank fishless and with plain silica sand, then our results with nutrient ratios could be somehow compatible. Naturally, only if we use RO+DI water mineralized with all nutrients following some coherent pattern. In all other instances the experience of any aquarist is largely individual, not directly applicable in different conditions.
 
Hi @_Maq_

I must apologize for not replying to your post #21 above. For some reason, it escaped my attention.

At present, I only have one tank in operation and the 'substrate' is simply a 2 cm layer of silica sand.

JPC
 
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