Re: Re: [RML] Planted Tanks

Bruce Hansen (bhansen at
Wed, 6 Aug 1997 08:32:46 +1000

I think Harro's point is that mostly plant growth success is more related
to limiting factors than it is to copious supply of any one factor.

Each plant needs N, P, K (Nitrogen, Phosphorus, Potassium) in the right
proportions for that species, plus trace elements, plus Carbon (usually as
CO2 from either air, dissolved in the water, or dissociated from
bicarbonate ions) plus the right physical conditions of light (of the right
intensity, perhaps also the right colour spectrum, and for long enough
hours per day) and temperature for healthy growth. Somewhere Iron fits in
there too, especially for tropical plants, and it seems that it is best
supplied in the substrate in a form that plants can access gradually but

Remember also that excess supply (or conversely insufficient supply) of any
or all will limit growth to a level determined by that factor in lowest
supply, so pouring more CO2 in will not help at all. The other major
problem often encountered is that of unwanted algae overgrowth - it seems
that excess P (usually as phosphate) and perhaps excess Iron and/or
Nitrogen that is not being used by the higher plants is the major fuel for
this algal disaster.

In the wild the seasonal water flow provides nutrients (even those in small
concenttrations such as trace elements) and removes metabolites - just as
our regular water changes do in aquaria.Conversely in the dry season as
flows decrease trace elements may be used up (unless abundant in the
substrate) and more importantly metabolites such as P and N are more
concentrated leading to algal blooms. A similar situation applies where
sluggish or still waterways are polluted by man-made excesses such as P
from fertilizers and detergents, and N from fertilizers and feedlots etc.

I was impressed in the NT to see how the "plant factories" of the wet
season go into decline as soon as the flow starts to shut down. I surmise
that even the continuous biological recycling of substrate organic material
causes no problems while the flow removes the excess nutrients. Obviously
this recycling process also supplies significant amounts of CO2.

Sorry about the length of this posting - but it seems difficult to be
concise on this topic.

bhansen at

> From: Harro Hieronimus <Harro.Hieronimus at>
> To: rainbowfish at
> Subject: RE: Re: [RML] Planted Tanks
> Date: Wednesday, 6 August 1997 7:00
> Don't forget that plant nutrition and plant growth does not depend from
CO2 or iron or phosphate or
> light or .... but from a sufficient mix of all. If you blow air into the
water by a filter or a membraneous
> pump, you also add CO2. If you then add iron and maybe other spur
elements (and of course lots of light)
> this may be sufficient for a normal plant growth. If you want to have a
strong plant growth it's useless just
> to take CO2, you also have to add iron and phosphate (which normally is
produced by the fish in sufficient
> amounts) and all the other things. The only success is that the plants
grow faster and won't survive if you
> take them to another tank where they don't get CO2 and all the other
concentrated nutrition.
> Harro