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Nutrient levels and limiting

Roger wrote:

> I'd really like someone to explain to me in substantial detail how the
> *absence* of an essential nutrient (P for instance) can be responsible for
> the nuisance-level growth of algae that absolutely *requires* that
> nutrient to be present.

Okay I'll bite:)
A plant needs a lot more of a nutrient ( say NO3) than the algae does. The
plant gets stunted at 1ppm or less for more than 3-4 days(a general range
for most plants). The algae just slows down but can still look bad. Example,
Green water. You can do a ton of water changes and be almost completely
certain there's next no NO3 (or PO4 for that matter)in there and watch your
plants wither(lack of NO3) yet the algae persist quite well. Next you add
NO3 to this tank and the plants do well and so do the algae. Kill off the
algae(via UV), add NO3 and the algae doesn't come back. Unless you let
things get too low. It may seem like it's absent, but the P and N are there
are lower levels we cannot detect and that are bad for the plants to really
make any headway for good healthy growth and uptake rates. But you can do
many many water changes and always have a slight haze even though you have
no NO3( at least that many folk's cheesy cheapy kits cannot test and that
even good kits can't also down real low 1ppm and less) in your water column.

Some glass algae can persist in absence of P. Plants certainly grow better
than algae can due to obtaining P etc from the soil(bacterial lysis etc &
PO4 complexes etc) but the algae can live on virtually nothing. Algae can
concentrate P at very low levels. Fish food is enough of a source for algae
to respond and grow to nuisance levels... but not the plants. Riccia
certainly does quite well with enough PO4. A number of other "difficult
plants" do very well in higher PO4 levels.

Most of the algae we hate has very efficient size ratios compared to the
higher plants. They can grow faster since there's less issue of transport,
most of the algae is a photosynthetic machine, no roots/xylem/flowers etc
that don't contribute to the production of plant mass. So it's ALL algae
production. We don't see the plants roots, xylem and other parts of the
plant. We see algae. A slow growing stunted plant( a deficient one) is going
to have a much harder time revving up and taking out the nutrients as fast
as the algae which always are ready to hit the ground running.
They take "no warm up". Plants that are healthy are closer to the same
"sprint speed" concerning nutrient uptake as algae. So algae doesn't not
bloom nearly as much in a tank like that. That's not all of it, I'm sure.
Some? I think so.  
But are plants truly slower or faster etc at this uptake?

But since algae can live in low and in high levels of nutrients and are
seeming more efficient, why do the plants continue to dominate? Algae is
still there but it's not dominating. There's plenty of nutrients for the
algae as well as the plants. Why then is this happening? It seems like a

Perhaps the tide is only tilted when there's a nutrient that too low rather
than this popular "excess nutrient" idea. Plants slow down and allow the
algae to gain a good foothold. Algae just doesn't get stunted like plants do
from too low nutrient levels. They bounce back fast. You can't eliminate
algae from limiting a nutrient down super low (there is not any real
absence, there's almost always a trace amount that's all the algae need to
show themselves in tanks often, were as the plants need far more to show
good growth, basically you can see the algae easier in response to nutrient
problems). They will be the first to use any nutrient when you add more back
into your tank. Plants can get stunted and weak. Algae? Stunted algae? Yes
you can hurt it some but it's still waiting for more nutrients to be added
back. Then when you do and add enough so the plants are not stunted anymore
you start to see a reduction in algae once again. Why?

 Our plants are all vegetative growth. If we had terrestrial plants, then
we'd see a sorry looking little flower producing it's little seed as the
nutrients run out so it can make it through till there's more
water/nutrients etc. Algae do the same thing essentially.

Roger had pointed to the plants "leaking" idea of perhaps sugars etc
leaching out and cause perhaps some inhibition of algae. But I've done
serious water changes........in effort to see if removal will encourage
algae growth of high nutrient levels without any effects( or at least
minimal effects) of any plant by products. I got even less algae after I re
added all the nutrients then did the same water change plus nutrient rebuild
each time. Plants grew like mad. What's up with all that? Next I kept asking
perhaps it's that darn substrate. I was not removing anything from there. I
could clean the filter, remove all the water etc. It was the only place
left. Something perhaps that was not being removed during the water
changes..........but what? Bacteria? Some chemical from the bacteria or
plant roots? Well whatever it may be it doesn't get effected too much by big
water changes.
The closer you get to an answer the further away it becomes:)
Oh well it's all just a guess anyway:)
Tom Barr