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
> 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