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Re: Algae control

> From: "Peter Hughes (X)" <peterh at pican_pi.csiro.au>
> 
> In the abstract it is mentioned that the micronutrients, N and K should 
> be in slight excess of P to provide algal control. I can see that this 
> may be true, but it should only be true if P then becomes limiting. If 
> the general feeding strategy/fertiliser reserves are high in P then it 
> will still remain in sufficient excess to cause problems.
>
	I agree entirely, and I keep a small fish load (so far) partly
so that I _know_ almost everything that goes into the tank.
 
> 
> A word of caution should be exercised here because the tanks that are 
> used as examples are exactly that. There are some problems with the 
> testing that should be pointed out:
> 1. the tanks are individual tanks and have not been duplicated in any 
> way. This may be seems a bit strange, but it is impossible to know if the 
> tanks would have gotten over those same algal problems by themselves. 
> This sort of experiment can probably only be carried out in a tank that 
> is divided after an initial period of running in, with the same planting 
> on each side. This is difficult to do but would give some valuable data in 
> terms of the difference in plant growth and what the algal population 
> differences are.
>
	I would really like to do some well controlled experiments, but
lack of time, money and space make it a bit difficult.  If anyone else
wants to do experiments, I would be very pleased, and would like to
hear the results.
	I am, however, pretty confident that the algae would not have gone
away by themselves.  I saw two highly undesirable (apparently) steady states
that were changed by doing something different in my tank.  The current
state is much better, appears stable, and reacts predicatably to substrate
disturbances.
 
> 2. Repeated addition of P to the, supposedly, P limited tanks and careful 
> observation of algal populations. Only by adding pure P over several 
> succesive cycles will show the dependency of algae on P. The fertiliser 
> tablets that remain undissolved in the substrate in case 2 may be 
> providing some other nutrient that sets off the algal bloom and not 
> necessarily P. The single addition of Phosphate and the resulting 
> observations do give a pretty clear indication about what is going on, 
> however it needs to be taken a bit further than it already has been.
>
	I agree.  I'm waiting for a while before I make any more P additions
to my tank, because I'm still pretty sure that there is a fair bit in the 
substrate. (effect of disturbance)  These effects are getting smaller,
however, as one would predict, and when they become _very_ small I shall
add controlled amounts of phosphate to see what happens.
 
> So what do I think of this evidence, I think that it is very interesting, 
> but stops just short of being proof. In saying this I am being a bit of a 
> devils advocate, but so much aquarium information is not really good 
> enough to be called fact (see recent discussions on the 
> useability/unavailability of ironIII in aquaria as an example). I have 
> started adding some K2SO4 to my tanks partly because of this discussion 
> and partly because I think that I have a K deficiency.
>
	I know it isn't proof, and I agree wholeheartedly about the 
quality of aquarium information, which is why Kevin and I presented
this as an hypothesis.  Would you please take measurements of the nitrate
concentrations in your tank now you are adding potassium?  I would like to
hear the results - I would predict a drop if trace elements are there.
 
> I hope that the authors do not take this as personal criticism, it is 
> not. I know how difficult it is to design experiments to prove something. 
> Their evidence also fits with general information here in australia. Our 
> soils are generally deficient in P and so that is the fertiliser that is 
> used and it is runoff from those fields that causes our algal blooms.
>
	I don't take it as personal criticism.  We posted this information 
because we thought it would be of interest, and to encourage experiment
and reporting of results.

	In retrospect, I wish I had written down, in detail, what I was
doing with my tank, and the observations I made.  I'm sure I lost a lot
because memory sometimes fails.  I would encourage others to keep a log,
preferably daily, and at any rate weekly, for each tank.

	Thanks for your interest.


Paul Sears     Ottawa, Canada