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Re: gluconate and other K sources

On Mon, 28 Jun 1999, Robert H wrote:

> I find this very interesting because I have been adding p.gluconate to a
> very densly planted tank with high intensity lighting, but have
> suspected that I also have created a high BOD. But I am confused as to
> what form of K I should be adding. I dont want to add nitrate...so that
> leaves sulfate? Murate of Potash? Is gluconate, gluconate? Is this the
> same stuff in Seachems Flourish products?

One problem with adding gluconate for potassium is that you end up adding
quite a lot of gluconate to get the potassium you need.  If you add enough
potassium gluconate to get 5 mg/l of potassium then you also are adding 25
mg/l of gluconate (assuming you're adding pure K-gluconate and there's no
extra gluconic acid or other gluconates in the mix).

I don't have any background info on the normal BOD or COD in planted tanks
so I can't say whether or not this is a lot, but it's certainly some and I
suspect that it is a lot.

I don't think this is much to worry about if you're using iron gluconate
tablets in the substrate once in a while, and it probably isn't a problem
with fertilizer solutions with gluconate like Flourish Iron, but if you're
using it to add large amounts of something then you might want to be

It has been mentioned here that chelating agents can bind with magnesium
and calcium.  If that's true and your water is very soft then it may not
be a good idea to add large amounts of potassium gluconate to your water.
The gluconate may tie up the small amount of calcium and magnesium
available and exaggerate any deficiencies you might already have.  The
calcium and magnesium would be released later as bacteria attack the
gluconate, but that could take a while.

As to other sources of K, potassium nitrate is the evident choice if you
want to add nitrogen as well as potassium.  Otherwise you could use either
potassium sulfate or potassium chloride more-or-less interchangeably.
It's probably best to use whichever will create a balance of ions in your
tank - if your water is high in sulfate or if you're already adding
something with sulfate, then you might want to use potassium chloride.  If
your water is high in chloride or you're already adding chloride with
something else then you may want to use the sulfate.  All else being
equal, the chloride would cause a smaller increase in total dissolved
solids than the sulfate.

Potassium bicarbonate would be an interesting alternative, but I don't
know that it is readily available.

Roger Miller