I said I'd leave this, and probably should live up to my
word, but I can't accept having words put in my mouth.

I originally used the word "cause", and promptly recanted
use of the word as overly strong. For the mistake of ever
answering a simple question, without perfectly refined
scientific word smithing, I'm sorry, again. I restated with
higher specificity, namely that P is one nutrient which can
serve as limiting. I offered Fe, "perhaps", to highlight
the non-exclusive selection of P.

Now, Bio 1, not even 101, teaches... "A Species will
proliferate unless, or until, it encounters a limiting
factor". A proper biological argument, surely any regarding
population control, is framed in terms of what "limits" that
species, and that species directly. When you do otherwise,
you open wider and wider ranges of potential causality.
Ignoring this "rule" is particularly dangerous in population
control, as you can end up putting multiple species in harms
way, caught between your problem population and it's true
limiting factor. In being non-specific you end up with
logic like - "If you kill Plankton, seals dwindle." Sure,
but I'm sure the Plankton is none too happy about your
choice of analysis, may they suggest you should just kill
the fish directly. From your office, you should know this.

You focus on your target and, culling from its requirements
alone, determine what can be limited. Work from there. So,
maybe we do have to kill the Plankton, but the argument is
properly stated "To limit seals, you can limit their food
(fish) or, perhaps, mating grounds; we can't control the
mating grounds well enough; so to limit fish you can limit
their food ..., etc."

Algae/BGA exists. If, as you claim, higher plants are
limiting, they are doing it through bio-chemistry. Name the
link. We know it is resolvable, routinely, in various
media, without nutrient starvation of the higher organisms.
Resolution/limitation (in tank) rarely depends on
predation, need not depend on antibiotic toxicity, and can
be accomplished regardless of lighting levels. Whine all
you want about PO4 "ain't it", Fe "ain't it", XYZ "ain't
it", but until you form a proper biological argument,
spelling out what factors ARE "it", I'll go with the
nutrient limitation, thank you.

Lighting is surely limiting, less light less stuff, but silk
plant tanks still do end up infected so "low light" is
hardly the complete answer. Temp is limiting, range
depending on species, but does the range 68-80 matter to
"our" species? Redox seems implicated, but a well lit,
reasonably clean, plant tank tends to maintain a serviceable
redox on it's own, and I've had BGA at high redox in my reefs.

Regardless, we all control light, temp, and less so redox as
a matter of routine. BGA/Algae comes and goes. It must be
resolving because 1) something in the water is killing it;
or 2) it is failing to find something else it needs (nutrients).

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wrote:

I feel I have spent enough time and supported my own arguments and
assertions, it's now time for you to look into things for yourself and
prove that adding PO4 to a planted tank causes algae.