Re: Algal Control article and Phosphates

First, my compliments to Kevin and Paul for taking the time for their
careful observations and to write up their experiments. This is the best way
to advance the 'science' of aquaristics and to facilitate healthy
discussion. The one change I would suggest is to include some information
about the chemical testing, including their lower limits of detection. I may
have more suggestions later.

As said by Peter Hughes,<peterh at pican_pi.csiro.au>, I agree that the
conclusions are true only if P is really the limiting nutrient. It is
conceivable to me that adding N, K, S and trace elements could help push
growth to the point where one or more of the trace element might still be
limiting. Adding a 'balanced' set of te does not necessarily ensure this.
Without a control in the experiment or a sensitive chemical test of the full
spectrum of chemicals, we do not know for sure. Also as said by Peter, "but
it is impossible to know if the 
tanks would have gotten over those same algal problems by themselves."

Nevertheless, the hypothesis seems reasonable and I also subscribe to the
philosophy that adding N and K will cause something else to limit plant
growth - very possibly P. To support the alternative hypothesis -- when soil
(and possibly other materials incl.laterite) is used in the substrate, iron
and magnesium would be adequately available in the substrate (at least for a
while). Reducing their concentrations in the water column will also starve

Regarding the effect of P, there was an interesting article published in TAG
which is an English translation of one originally published in AquaPlanta
(see TAG, V7n1). The author, Peter Peterson, slowly reduced phospahte
concentration by adding a 0.3% solution of of iron chloride (over 8 day
period). He reduced the Phosphate concentration to 0.1 ppm. During this
time, he observed that some species of higher plants started to suffer and
algae bloomed. This suggests that his algae was able to utilize phosphates
at a lower level than some of his plants. He observes that the results may
be species specific.

With extra feeding he brought the conc back to 0.6 and deficiences vanished.
He concludes that a range of P concentrations may be optimal for good plant
growth without algae. He thinks that 0.2 ppm is too low. The article had
many other interesting obsevations about levels and different types of
aquarium plants and growing conditions. The above also supports Peter who
said "Only by adding pure P over several succesive cycles will show the
dependency of algae on P"

Neil Frank, TAG editor    Aquatic Gardeners Association    Raleigh, NC USA