Algal control in the aquarium


I would like to offer a few observations and comments about the lengthy 
treaty that we just received on algal control. It was very interesting to 
see that someone has gone beyond conventional wisdom and tried something 

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 definetly agree with the statement about the lack of good information 
on what water quality perameters are able to be "tweaked" and also the 
important ones for impending trouble.

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.

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.

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 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.

Peter Hughes