There is a small debate going on on another forum about whether or not potassium is removed from the water by the plants continuously like N and P are. Or, is just enough potassium removed to build up the needed concentration of K in the plant cells, and from then on none is taken up? The contention is that dosing KNO3 as we do will cause a continuous rise in the potassium level in the water unless we do regular water changes to remove it, even if the plants are using up all of the NO3. If so, then even the lean fertilizing folks should be doing routine water changes.

Well, it's species dependent for one thing.
We keep 300-400 species.

I really never like generalizing too much there without putting that out there.

I'd say enough to maintain the levels inside the plant, the endogenous levels.
Plant K+ transportor uptake enzymes will adapt over a very wide range as concentrations increase or decrease(given a little time).

So plants adapt to a wide range of K+ concentration, just like light levels, CO2, NO3, P and so on.......

The professor here at UC Davis is by and far the world's expert on the K+ transportor and research in plants. Intense guy. Grill me once, I got lucky and had the right answers

When folks debate, they might wish to look some more into general plant molecular genetics, as most of the Physiology has transferred into that area, rather than measuring uptake rates of plants.

A lot more occurs than what you can merely see in the external water column.
What about roots?

What about other ions like sodium and it's effect on K+?
How about NO3 as a counter ion inside the tonoplast?

Well, back to the main issue here about water changes.
K+ has a very wide range before it becomes toxic.
Likely over 100-200ppm range.

I've never pushed it past 110ppm.
But I had great results with and wide range of so called sensitive plants, so did Erik and other folks in the SFBAAPS club 10 years ago.

So even if you did a lean routine, I do not think it would build up much and certainly not infinitely.


Here's why and the answer is very simple:
What goes in, must come out.
This is a 2 box model.

So even if you never do a water change, folks remove dead leaves, they prune and sell plants out of their tanks? They still clean filters?

Plants concentrate and maintain much higher internal levels of many nutrients, when we hack them back, we are in effect, EXPORTING this out.

In lean aquatic ecosystems, most of the nutrients are not in the water, rather, in the plants, thus the plants define the system, not the water column so much.
Or they might be in the sediment where none of these folks on this "other forum" seem to be able to test or measure

So the water column is merely 1 or at least 3-4 aspects they are not even considering. Buy a good K+ test kit, eg a colorimeter.

Regards,
Tom Barr