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Re: Potasium Gluconate Worsens Cyanobacteria?

On Wed, 5 Jan 2000, Sherman Lovell wrote:

> 	The hypothesis:  I'm wondering if potassium gluconate might worsen a
> cyanobacteria problem.

Algae too, for that matter.

> When I add 5 potassium gluconate tablets to the
> tank, most of what I'm actually adding (by weight) is glucose, a simple
> sugar.

Don't get too carried away with the similarity in names.  Potassium
gluconate is the potassium salt of gluconic acid (C6H12O7); there isn't
any glucose involved except in the manufacture of the gluconic acid.  Just
the same, it seems inevitable that the gluconate would be bacteria food.

> This has always kind of bothered me.  Somebody in the tank has
> to eat up all that sugar, and I'm wondering if maybe it might be the
> cyanobacteria.  (You could run an experiment where you try to grow
> cyanobacteria in tank water and glucose with no light I suppose...  I
> remember from my days as a microbiology major that lots of bacteria are
> very adaptable in this sort of way.)  Anyway, I thought I'd just throw
> out the idea for consideration.

I've toyed with the idea a bit, but I wouldn't say that I ever raised it
to the level of theory.  I have read that algae can live on organic
compounds in the water.  Cyanophytes should have the same capacity.

I even went to the point of asking a biology professor at UNM whether
dissolved organics can be used by algae to the extent that it might cause
algae problems in aquariums that otherwise wouldn't occur.  The professor
has an interest in dissolved organics in aquatic systems.  His reply
indicated that normally ("normal" in this case would be natural
conditions, not necessarily aquarium conditions) bacteria should
outcompete algae for organic nutrients in the water.  I think that
cyanophytes would also normally be outcompeted by true bacteria since even
though cyanophytes are prokaryotes they are not primarily heterotrophic as
are many bacteria.

Aquarium conditions may be different enough from natural conditions that
observations of "normal" behavior don't apply.  Some problems could be
partly explained if simple sugars and other readily metabolized compounds
can be linked to cyanophyte and algae outbreaks.  The metabolizable
compounds might be added by the aquarist (as gluconate, for instance) or
released by plants.

> 	The anecdote:  My job briefly got in the way of my aquarium interests,
> and my overstocked, overplanted, undermaintained tank developed pretty
> high nitrates (20+ ppm -- high for me).  Cyanobacteria started growing
> along the glass/gravel line.  I started adding potassium gluconate and
> the nitrates dropped (I was very pleased about this -- it was right out
> of Conlin and Sears), but the cyanos just kept on growing.  (They do
> seem to behave in a somewhat "infectious" manner, in that once they get
> really established, they're much harder to control.)  I'm wrestling
> things back under control now, but I can't help wondering if that 500
> gram dose of sugar every week didn't make things worse.  Just a
> thought.  In any case, I'm not going to finish using that bottle of
> potassium gluconate after all.  I'm going back to KCl.
> - -- Sherman Lovell

You might also want to make sure that you maintain good circulation in the
tank and that the many plants are growing (not just healthy-looking) and
free of other nutrient deficiency symptoms.

Roger Miller