Re: Algae control
To: Aquatic-Plants at actwin_com
Subject: Re: Algae control
From: psears at NRCan_gc.ca (Paul Sears)
Date: Wed, 3 Apr 1996 09:03:45 -0500 (EST)
In-Reply-To: <199604030839.DAA26575 at looney_actwin.com> from "Aquatic-Plants-Owner at ActWin_com" at Apr 3, 96 03:39:02 am
> 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