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Re: PO4 Deficiency & CO2 Swing

Alex R. wrote:

> I don't have a PO4 test kit so I'm just speculating all this. Is it
> reasonable to assume my plants are PO4-limited if the growth is this slow
> they don't pearl a lot? BTW, I have a 30 g. tank with 96W of lighting and
> Flourite substrate.

Adding one nutrient while holding all other factors constant is one way
of testing for a limiting nutrient.  If you are sure of your response,
then it sounds like you identified a phosphorus deficiency.

The "classic" symptom of phosphorus deficiency in terrestrial plants is
a purple-ish discoloration.  I don't think I've ever seen that happen in
aquarium plants.  I have had plants and tanks with problems that were
fixed by adding phosphorus, and the symptoms didn't include
discoloration.  Growth stopped or slowed dramatically; over time the
plants (vals, in particular) became stunted, and a sort of filamentous
algae started growing on (but not actually attached to) the most
effected plants.  Pearling still happened, but mostly after a water
change and I really couldn't tell whether it was the plants that were
pearling, or the algae.

Phosphorus is used by plants (and other things, for that matter) in
every aspect of their growth and metabolism.  It's reasonable (to me,
anyway) that a phosphorus shortage would cause a gradually worsening
shutdown of all growth and other functions.

> One reason I'm asking is because I have a huge filamentous algae outbreak.
> Don't ask me if it's BBA or hair algae. I don't know, but there seem to be
> several types. And if I do in fact have very low PO4, it hasn't done much
> against the algae. It currently covers all my plants because of their slow
> growth. I have stopped adding micronutrients three weeks ago. I also have an
> Fe test kit, and when I was adding micronutrients, the amount of Fe was less
> than 0.1 ppm. So what would you recommend?
> Should I restart the micronutrients?

When I identified phosphorus as the problem in that tank, I cleaned out
as much of the algae as possible, continued to add small amounts of
phosphorus (in my case, using Hagen PlantGro) and maintained everything
else as usual.  The plants started growing and the algae didn't come

Roger Miller