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Re: po4

Arthur wrote:

> I'm not sure that a lot of useful conclusions can be
> drawn from the experiment described in the article.

In fact, be very careful trying to extend any conclusion from marine
research to a freshwater aquarium.  While Dr. Hovanec did throw in the
occasional mention of freshwater, the research he sited was in open
ocean settings - not even coastal settings.  I don't think his
discussion can be reasonably extended to a natural freshwater
environment, much less to a freshwater aquarium.

> Also, I am not sure what they mean by the threshhold
> amounts of N and P that algae require.  Does it mean
> that when you have reached those levels you should
> have lots of algae?  Or just detectable algae?  How
> were those numbers derived?

I couldn't find any use of the term "threshhold" or "threshold" in
Hovanec's article, so I'm without context.  Perhaps the term is being
used to describe the minimum concentration necessary for a population to
maintain it's existing size.
> "it is extremely doubtful that nitrogen and phosphorus
> are at such low levels in aquaria that they limit or
> prevent the growth of algae."  Do they imply that
> there is no utility to keeping your N and P at low
> levels?  What if your N and P double?  Triple?  Should
> you be already above threshhold values, will it make a
> difference?  I believe so.

The "low levels" that Dr. Hovanec refers to seem to be 1.4 mg/l total
nitrogen and 0.3 mg/l total phosphorus.  Those values correspond to more
than 6 mg/l nitrate and almost 1 mg/l of phosphate.  Nitrate and
phosphate may well be the only significant forms of dissolved nitrogen
and phosphorus in a well-polished planted tank.  Levels lower than those
are very commonly reported in planted tanks; in fact those values
wouldn't even be considered low.  If all we had to do to control algae
was to keep the N and P levels below 1.4 mg/l and 0.3 mg/l,
respectively, then controlling algae would be a piece of cake.

> The article implies that the greater body of
> literature supports phosphorous as the most important
> limiting factor in freshwater.

This is an old and common generalization.  You can find examples in the
literature were pretty much any potentially limiting factor was found to
limit algae growth.  Generalizations like "phosphorus is the most
important limiting factor in freshwater" may be true, but they are
without value when applied to specific conditions, and certainly without
value when applied to an aquarium.

> What we lack are rigorous experiments.  Or even
> semi-rigorous.  Our tools of measurement (test kits)
> are crude.  To be more accurate in experiments, we
> should setup fishless tanks (no fish food),
> reconstituted water, and strictly controlled inputs,
> with control tanks under the exact same conditions as
> the experimental tank.

I don't think that rigorous or even semi-rigorous experiments do us much
good.  Most of us don't keep aquariums in a conditions that comes
anywhere near the conditions of a well-controlled scientific experiment
so it would be difficult to apply the results of such an experiment. 
Perhaps it would be more useful if we stopped trying to extend
observations from natural settings to application in our home aquariums
and instead started relying more on our own experience and observations.
> One interesting phenomenon that I have observed in my
> own tanks is that algae when moved to an algae-free
> tank usually dies quickly.  What makes this so?

Algae are highly evolved specialists.  They tend to thrive in one
tightly defined set of conditions, and not elsewhere.  Algae are
difficult to successfully trans"plant", even if you have tried hard to
make its new home supports other algae and the setting appears suitable
for its growth.

> Enough rambling.  Just a call for science.  More of
> it.  And more art too.  :)

Science.  Where there is money, science follows.  If you could assemble
the money necessary for research you would find that there's no shortage
of qualified people who are eager to do the work.

Roger Miller