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DO and CO2 and algae

I'm at it again:) Yammerings from the swamp:)
Algae and lack of it's presence in a nutrient rich stew:

A}
The high light tank:

Folks have said that algae can be limited by low/absent nutrients.
The nutrients (NPK) are all available to the algae in my tanks(and other
folks as well) and they are available to the plants. The levels are quite
rich by algae terms yet no algae. The same tank with no P still can have
algae presence even if you limit the nutrients in attempts to starve the
algae. So limiting seems not to do much. It hurts the plants, and perhaps
slows the algae some but it will not solve the long term problem.

Roger had considered the sugar leaking notion or we could say chemicals of
some sort leaked into the water by algae or plants helps them to exist. I do
big water changes frequently removing this so I see little effect(s) from
that. Also, it would/could be plant specific. Some plants would leak worse,
some better etc. Some algae would fair better and some would not. I suppose
one could argue that a general fast growing plant would leak more than a
general slow grower but I think it's even more general than that.
I have not seen evidence to support the claims of alleopathic chemicals
causing problem in tanks that receive regular water changes. They'd have
spew out large volumes to have any effect when I'm doing 50% weekly water
changes and sometime more.

I just believe it has to be a general thing that causes the algae not to
grow. I know the algae does not do well when the plants do well. That we can
all agree on. But why? They both have the same access to the nutrients
either way and have much of same bio-machinery/needs.

I've said this before and almost got a O2 bottle to try this out: still
might. 

I think perhaps high DO levels combined(or not) with the CO2 levels is the
cause. At high DO levels even in high nutrient places/environments the algae
typically would be at a disadvantage if it started growing since some other
algae (or plant) is doing well(and producing all this DO). The CO2 allows
the plants to act in this capacity as massive DO producer and they take a
little time to get going and do this(this provides a window of opportunity
for the algae to grow in some cases). Algae also have a problem when the C02
is well supplied in nutrient uptake. Many algae grow quite well in enriched
CO2 grow tanks. But they do not use the Carbonic anhydrase(CA) enzyme when
this is done. 
It's production is only inducedable when the CO2 content is low. They go
after HCO3 then. Some plants do this as well.
The CA enyzme may be linked to the DO "sensor" gene or some where along some
pathway. When the CA is inactivated and/or the algae senses high DO it sits
out and waits(and you get no algae as a result). These two may or may not be
linked. But I think they are best canidates for why algae doesn't grow in a
high light tank with plenty of nutrients available(like my tanks). My DO's
run up to 13-15ppm.

At high DO levels even in high nutrient places/environments the algae
typically would be at a disadvantage if it started growing since some other
algae (or plant) is doing well(and producing all this DO).
 
Algae have incredible abilities to concentrate ions in water with very low
concentrations. They can live in much more deficient waters. Plants are not
so fortunate. They need more.

Poor DO means nothing is growing in the water to the algae's "brains". This
means it's a good time to grow since nothing else is present. It's a bad
time to sprout when there's something else already established.
Limiting nutrient do come into play to some degree but these are very low
levels and are unrealistic IMO to our nutrient rich tanks.

The limiting approach CAN be used when you just need to finish the algae off
a "little bit". Once completely run into the dirt, your fine and have more
wiggle room with your nutrients.

B}

Now about growth rates and speed.
A slow growing 2 watt a gallon tank may benefit from a limiting approach
since the plants grow slower. The amount of nutrients is lower but the
plants do not need as much either. So they do not get stunted by
deficiencies(nearly as much). They may also do better from chemical leaking.

So what'd I do?
I tied this on my slow growing lower lighted tanks also:) Both a 1.6 and a 2
watt a gallon tank. With good higher levels of CO2(20+ppm) and slightly less
rich stew(.5ppm of Fe not 1.0ppm, same N,P and K) I found great results
again. So I have hard time seeing the reasoning behind the slower growth and
limiting actually doing much there. P and N uptake was slower but I reset
the tank each time I do a water change. So that never was an issue. Again
big water changes to remove any bio chemical warfare.

Regards, 
Tom Barr