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Re: algae


I've been following this thread since Arthur first posted his observation
on how disturbing the balance in his tank lead to algae outbreaks and
returning to balance seemed to cure them.

Before going any further, I'm going to howl at the moon yet one more

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.

On Tue, 3 Jul 2001, Arthur wrote:

> 75gallon tank with CF 96w x 1, 55w x2.  Pressurized
> Co2, diffused (Eheim-style Japanese product).  As far
> as Co2 levels, about 1.5 bubbles/sec.  I wouldn't call
> it high co2.  More like medium.  Not as much pearling
> as their could be.  (I have pH test kit and KH, but
> lost instructions and charts, have reordered booklet).

As far as testing levels is concerned, I think that may just provide bits
of technotrivia that may never tell Arthur what happens in his tank.  The
original "balance" desription -- while nebulous -- may provide a better
explanation for Arthur's algae outbreaks than he will ever get with a
reasonable use of test kits.

The balance that we are concerned with is a dynamic balance; it's a
balance of different rates.  We add nutrients and carbon through feeding
and dosing at a particular rate.  Precipitation, plant growth and algae
growth take the nutrients out or the water at another rate determined by
conditions in the tank.  The concentrations that we can measure in the
water increase when we add nutrients faster than the plants remove them,
and the concentrations drop when the plants remove nutrients faster than
we add them.

Our tanks are at a happy balance when the nutrient rates in and the rates
out are equal and herbivory, competition for light and tank cleaning
maintains plants (rather than algae) as the dominant producers.

The dynamic balance tends swing back and forth around an average, much
like the mythical "balance of nature". If Arthur does anything to his tank
that reduces the rate that plants use nutrients -- pruning for instance --
then algae growth can increase to fill the void and that restores the
balance between nutrients added and nutrients used.  Of course, that's not
an adjustment that we usually want to see happen.

Small swings are inevitable and not usually much of a problem.  I think
the basic problem with Arthur's tank is that it's a high light,
CO2-supplemented tank with (as a discus grow-out tank) a big rate of
nutrient influx.  There has to be a high rate of nutrient use in the tank
to balance that influx.  Even a small temporary reduction in the nutrient
uptake rate by the plants can cause nutrient levels to spike.  The
concentrations return to normal when growth rates resume, but in the mean
time the algae have taken hold.  The spike may last no more than a few
days before levels return to normal, so Arthur might have to test daily to
even see the spike.

Algae growth rates are probably just about exponential; the more algae
there is, the more algae growth there is.  So just a brief pulse in the
algae growth rate to give a larger algae population quickly translates
to a nuisance problem that doesn't automatically disappear when the
nutrient spike passes.   Herbivory, tank cleaning and other measures are
necessary to get the algae back under control.

> I might also add that I do not supplement K either.  I
> used to, but it felt like voodoo, since I wasn't
> replacing an obvious nutrient deficiency, and there
> was no way to measure it (i.e. to know if I had a
> deficiency).  It's like one of my old uncles told me,
> keep it simple stupid.


I found (from my water utility) that my tap water only has 1 mg/l K.  I
assume that isn't enough.  I add KCl to the water I use for water changes
so that my tanks should be getting around 10 mg/l.  I think that's enough.
No testing.  Simple.

> I appreciate those that really
> delve into the technical aspects of fertilization, but
> I am of the more practical variety, that just wants
> the plants to look good for as little headache as
> possible, so I can move onto the aesthetic tasks of
> making the arrangement look good.

Nice goal, and a significantly different goal from wanting to grow
anything that will burgeon under water.

> When people who are
> new to the hobby read a thread that is very in depth
> and complex with regard to fertizilation, I can't help
> but believe they might find this hobby a bit
> intimidating ("whoa!  too complicated!  I think I'll
> stick with my nano-reefs!").

Well, this is a fairly advanced list.  There might be better ways for
beginners to get their start then by reading APD.

> It is possible to have
> success (luck?) without thinking that much.  But
> having said that, the science behind algae control is
> important and deserves scrutiny.  What we lack are
> controlled experiments.

Certainly be my guest.  I think it would also help if we had more
good tests, some way of accounting for microbiological effects and organic
chemicals and sometimes just more logical analysis of our observations.

> I propose that someone (maybe myself) puts together
> two identical tanks, from scratch.  No fish.
> Carefully recorded inputs.  Identical substrate,
> lighting, etc.  And then attempts to *induce* algae
> breakouts, by tinkering with variables, such as plant
> load, macros, co2, micros, water changes, etc.  One
> year of this might tell us more than much of our
> collective "in my experience"'s combined.

Maybe, but it's been proposed and to a certain degree it's been tried.
Aquariums are complicated systems, and the possibility of getting
dependable results out of a long-term test of that sort is fairly low.

Another technique that is perhaps more practical is just to quantify
important mechanisms in the tank and to use basic principles to figure out
what the numbers mean to your aquarium.  Mass and energy balance provide
the physical basis for that kind of study.  Ecological studies provide a
wealth of examples.  Diana Walstad's calculations of nutrients supplied by
fish feeding is another example of that approach.

Short-term experiments on simplified systems tend to give more dependable
and reproducable results then long-term experiments on complicated
systems.  The problem is then to interpret those simple results in a way
that's meaningful in the real world.  That is how science advances.  A
hundred people run a thousand simple experiments and they collaborate or
compete through conferences and journals to put it all together into a
cohesive picture.

Here's a simple experiment that serves as an example.  Back when this
thread first started I went off on a tangent and theorized that lighting
was more important than nutrients for controlling algae.  I thought that
if that were true then my aquarium water should be loaded with more than
enough nutrients to support a lot of algae growth; I should be able to
take water out of an "algae-free" aquarium and place it in sun light and
the algae population would explode.

It's a simple test, so I did it.  This is the third day of the test and
this morning the water was still as clear as it was to start with.  Live
and learn.  I think.  Maybe that means the one or more nutrient levels are
too low to support algae growth, or maybe there's some other reason why
the water didn't turn to pea soup.

Roger Miller