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Well, I snipped about as much as I could and this still got really, really
long.  I hope it's worth it :).

On Wed, 29 Mar 2000, Steve Dixon wrote:
> Roger Miller's response to Michael Rubin's "what is missing" comment
> has stirred me up quite a bit this morning.  So I thought I would
> share some of
> my thoughts.  No personal attack on Roger is intended in any sense; in fact,
> I'm delighted that Roger has "forced my hand" so-to-speak, and made me
> rethink some of the rationales for my own views!  :-)   Roger's comments are
> in quotes and my responses follow.

Gee, always glad to be of service :)
> Roger:
> "A lot of people on this group when faced with an algae problem (their own
> or that of others who they are trying to help) have fallen into a similar
> conceptual trap; they ask "what's missing?"
> The answer to the question is patently obvious.  THERE IS NOTHING MISSING.
> If some essential component were missing then the algae wouldn't be a
> problem."
> Me:
> I suspect that Roger may be right on this point about half the time. ;-)
> Roger's note seems to be saying if you have an algae problem, ONE OR MORE
> NUTRIENTS MUST BE IN EXCESS.   (This statement is nothing more than a
> necessary corollary of Roger's "nothing is missing" statement. Let's call
> this Roger's Corollary! :-))

Hmm.  I hope that name doesn't get propogated, because I don't think I
agree with it.  For one thing, nutrient concentrations may not be the
cause of the algae problem at all.  For another, if we're going to take
Leibnitz' rule to it's extreme, when one nutrient is growth-controlling
then ALL other nutrients are present in excess.  That fact is of rather
trivial value because excess nutrients aren't usually a problem.


> Back to Roger's original "nothing is missing" statement.  What is Roger's
> scientific justification for that statement?  Answer: Leibniz Law, which
> states that the limiting growth factor will limit plant growth.  According
> to Roger, nothing is missing because the algae is growing!!!

Actually, the statement doesn't depend on Leibnitz at all.  It's based on
the composition of the algae.  Certain elements are essential for the
existence and growth of algae (and plants for that matter).  The algae
have to contain all of them, or the algae isn't there.  My statement is
based on the simple fact that if the algae is there then all of the
nutrients that are essential to its existence are also there.  This says
nothing at all about growth rates.  And yes, it is tautological that for
the algae to grow, all of its essential nutrients must be present and
available to the algae.  That is the definition of "essential nutrient".  
The same thing applies to plants.


> Why aren't the higher order plants growing?  That should be the focus
> of our inquiry.

Did someone say that the higher order plants weren't growing?  Plants can
grow quite well in the presence of algae.  If they aren't, then there
might be quite a few reasons why not.

[more snips]

> Roger supposes a tank that
> is nitrogen-limited, but has enough other nutrients.  He says that nitrogen
> limits both the growth of algae and higher order plants.  He says that
> increasing nitrogen will "certainly [result in] more growth from the algae."

Actually, if it doesn't, then nitrogen wasn't growth limiting to start
with.  The functional definition of the growth limiting nutrient is "the
nutrient that when added produces the largest change in the rate of
growth". This definition doesn't depend on Leibnitz.  I think the
definition can be attributed to Gaudy and Gaudy (Environmental
Engineering, McGraw Hill, etc. etc).

I'm not sure I want to keep dragging Karen into this, after all she's
perfectly capable of speaking for herself.  Just the same, I recall a
thread a couple years ago where she agreed that some people who undertake
additions of potentially growth limiting nutrients *do* see initial
explosive growth of algae.  In those cases where they don't, either they
added the wrong nutrient or the tank passed through the "explosive growth"
phase and back into nutrient limited growth quickly enough that it wasn't
a problem.  I think this latter conclusion may have been my conclusion
rather than hers, but I can't recall for sure.

> We have observed for years and years now that increasing nitrogen in
> nitrogen limited situations will REDUCE ALGAE GROWTH, and increase higher
> order plant growth.

Some people have reported success with this method, and other people have
not.  Where it does work the reduction in algae growth is thought to be a
secondary effect of causing some other nutrient to become limiting, plus
the tertiary effect of competition.  It isn't a direct effect of adding
nitrate.  As in most cases where the solution is indirect, results can be
inconsistent.  A more direct approach would be to reduce the concentration
of some other dissolved nutrient (phosphorus, for instance) to the point
where it becomes growth limiting.  Since this is a direct approach the
results should be more consistent and predictable.
> As an aside, when Claus Christensen was here on the West Coast, while he
> paid homage to Leibniz, he went on to say that in practical terms Leibniz
> law was somehow wrong.

I think there are quite a few possible problems with Leibnitz, especially
when applied to individual plants or to short periods of time.  It is of
course completely wrong if you apply it to a case where nutrient
concentrations aren't growth limiting.  Right or wrong this lists has a
fairly long history of depending on it as a fairly simple model that
explains some of the conditions we see.

> While I can dream up limiting factor theories that might explain why
> higher order plants seem to be able to "outcompete" algae, in all
> honesty I'm completely baffled by the notion.

If you go back to the Davis and Brinson article, there's an article that
shows (again, for natural conditions) that under oligotrophic and
mesotrophic conditions - low to moderate production rates, generally with
low dissolved nutrient concentrations - that plants compete very well with
algae.  Algae do better under eutrophic and hypereutrophic conditions
where total production rates are higher and dissolved nutrients are
generally higher.  I can think of several specific mechanisms for that and
some might actually be relevant to aquariums.


> Test kits can be an invaluable aid to tank observation.

I've got some successful, well-planted tanks that I've never used a test
kit on.  I've got another that I haven't tested for anything in 5 years or
so.  This is a hobby and I encourage you to spend your time in it in any
way that gives you the greatest enjoyment.  You may find them invaluable;
I find them mostly dispensible.  And yes, I do have test kits and I do
occasionally use them.

[did I snip something here?]

> While it is true enough that if the growth is robust and healthy the
> nutrient supply is fine, how do we know by visual observation alone
> what the problem is if the tank is a wreck? You suppose, wrongly in my
> view, that some or other nutrient is always in excess (if the algae is
> growing).  But which nutrient is it and how do you tell the difference
> between one excess nutrient and another.

Um, if the plants aren't growing well then probably nutrient excess isn't
the problem.  Unless of course it has reached toxic levels or caused such
imbalance that usual nutrient uptake is disturbed.  In that case there
should be symptoms.

> Or heaven forbid, combinations and permutations of multiple excess
> nutrients?  The mind reels.  I wish I could do that but I can't, and some
> times my test kits help me eliminate certain issues and improve the
> likelihood that a particular course of action will help the aquarist with a
> problem.

I'll give you this.  Test kits can be useful for trouble shooting.  So can
careful observation of the plants, and a review of changes and maintenance
practices in the tank.  My preference is to get as much as possible from
direct observation, and to test only occasionally.  This is certainly a
different case from using test kits in the regular micro-management of a

> Claus Christensen and I talked non-stop for 10 hours last
> Thursday as we drove to and from and toured the Monterey Bay Aquarium.

I'm envious.

> We talked about potassium at some length and I was surprised to hear
> Claus say that many if not most of our aquatic plants do well with 10
> - 15 ppm potassium, but that several species do much better with 25 -
> 35 ppm potassium in the water column.  So to answer your specific
> question:  They just might like the extra potassium :-) which is not
> to say it might be just as well to add some potassium in the
> substrate.

As I recall, Tropica's plants are grown hydroponically.  It makes sense
that the hydroponic solution would be similar in composition to soil pore
water.  I'm not sure my fish want to live in a hydroponic solution so I
try to restrict high nutrient levels to the substrate.
> While I hate to be the bearer of bad news, I can report more or less for
> sure, that 20 - 30 ppm of potassium in the water column is not necessarily
> EXCESS and in an otherwise well-run aquarium, presents no algae issues that
> I'm aware of.  

None that I'm aware of either.  Excess nutrients aren't a problem unless
they reach toxic levels.  *With* the simplifications of Leibnitz' rule and
*if* nutrients are growth-limiting, and *if* the growth rate of algae is
high enough to become a nuisance then it's because the *limiting* nutrient
-- not any excess nutrient -- is too readily available.

> It occurs to me that perhaps Roger has his own version of "magic Marin
> water" and so he naturally thinks about excess nutrients, while those of
> working with very soft pure waters constantly think about what nutrients to
> add!  

Certainly there are different approaches required for hard water and for
soft water.  Unfortunately my water is soft, but far, far from pure.

Thanks, Steve for the exchange.  It's been a delight.

Roger Miller