Re: Algal control in the aquarium

On Wednesday, 3 April 1996, Peter Hughes wrote:

> 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.

Very true.  For large values of P, the lighting could become the
limiting factor.  For even larger values, an aquarium packed to the
gills with plants growing at their maximum rate would not be P
limited.  Fortunately, this situation is unlikely to occur in an
aquarium unless uncomposted manure is used as the substrate.

> 1. the tanks are individual tanks and have not been duplicated in any 
> way.

We're working on this.  A number of individuals are now attempting to
reproduce our results.

> 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.

We've been careful to point out that our experiments were uncontrolled.

> 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 may repeat the the phosphate experiment, but it's such a shame
to create an algae bloom in a nearly algae-free tank...

> So what do I think of this evidence, I think that it is very interesting, 
> but stops just short of being proof.

We're not offering proof.  We're offering a hypothesis that fits our
observations.  It's a very testable hypothesis, and we hope others
will be inspired to continue the work.

> 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).

Very little of the information out there is good enough to be called
fact.  The paper is partly in response to the lack of good information;
we're trying to get people pointed in the right direction.  Endless
debates don't prove anything; careful experiments and observations do.

> I hope that the authors do not take this as personal criticism, it is 
> not.

Criticism (preferably constructive) is an important part of the excercise.
Without it there can be no progress.
Kevin Conlin   kcconlin at cae_ca   "We're Canadians.  We HAVE to be polite"
Finger as332 at freenet_carleton.ca for PGP public key.