[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Simone's substrate and river water


First, from Simone: 

> Roger said that laterite will probably dissolve if mixed with humus and
> peat, that because of a possible low redox potential of my substrate and of
> a very low Ph.
> That seems right to me and  I will probably not use laterite also because
> it is not cheap (Dupla). But humus taken from a garden supply that is said
> to be almost completely pure should not contain undecayed organic material
> and that mixed with a very small amount of peat, that is very resistant to
> decaying, probably will not result in an high-oxygen-demand-low -ph-soil so
> I should not have very low redox potential, the heating cable can also
> oxygenate the substarte very slowly keeping a stable redox potential. Am I
> right?

There's something I forgot to mention with a laterite/organic matter
mixture (a caution that Simone apparently doesn't need).  Laterite
normally contains a large amount of aluminum.  Aluminum becomes toxic to
at least some terrestrial plants when the soil pH drops below about 5.5. 
I expect that aquatic plants would respond similarly.  If you use 
laterite you need to guard against low pH.

Without circulation in your substrate, I expect that even relatively
stable organic matter in high concentrations could lead to low redox
potentials.  That is not necessarily a bad thing.  The pH effect isn't
real dependent on the redox state.  Peat is used in gardening partly to
lower soil pH.  Some peat products can have pH as low as 4.5.  Before you
use the peat in your mix you may want to test it:  wet the peat with some
distilled water and let it set for a few minutes, then squeeze some water
out and test with a normal pH tester.  If the water is too darkly colored,
you might have to use a paper indictor instead of a liquid indicator. 

I haven't used heating cables with an organic substrate.  I use a UGF 
plate under the substrate, and pump water from it at a very low rate.  
I'd be interested in hearing success stories/problems from people who 
have used heating cables in organic substrates.

> Probably I will be able to try to make a layer of laterite above the
> humus/peat/vermiculite mix but I wont be able for a long time to prevent it
> from mixing 
> About  the gravel I will use 2-3 mm gravel that should not mix very fast
> with the soil under it. But I can mix some kind of vulcanic gravel with the
> lower layer if you think I should Roger.

I found that helped keep the humus and peat from moving and I think it
limited the amount the stuff would compact.  But this isn't one of those
critical things that will determine your success or failure.


Then from Frank Reiter:

> > Plants and algae grow when there are enough of *all* the necessary
> > nutrients available. If one nutrient is not available in sufficient
> > quantity, growth slows or stops.
> Yup, I've got that.  I guess I just have trouble thinking that there was 
> excess phosphate available in this river.  I have heard before concern 
> about high nitrate levels in natural bodies of water.  Is it common for 
> phosphate (or some other source of phosphorus) to be plentiful in these 
> water bodies?

Phosphate is most often the limiting factor in natural water bodies. 
Pollution from municipal and domestic wastes can increase phosphate enough
to make something else limiting.  Also, there are areas in Florida (and I
don't know where these springs are) where phosphate is mined commercially. 
Is it possible that the springs in question drained from one of those
areas and so has naturally high phosphate levels? 

It has been several years since I did a lot of reading in limnology.  At
the time, most of the detailed information on water quality and nutrient
controls on plant growth seemed to come from the upper midwest US, nearby
parts of Canada, and northern Europe.  Since then I've repeatedly come
across references that identified the controling nutrient as something
other than phosphate.  In the one case I worked on locally, I concluded
that nitrate rather than phosphate was the limiting nutrient - inflow to
the reservoir was polluted and phosphate levels were simply too high to be

> > Now, the big difference between streams and aquariums. A plant in a
> > stream is bathed in a constantly changing flow of water. It doesn't
> > matter that nutrient levels are lower than we have in an aquarium
> > provided the water keeps flowing, bringing a fresh supply of nutrients
> > every second.


> As you say, others have maed this point before, and at first I accepted it 
> as sounding logical.  After some thought though it just doesn't make sense 
> to me.

I'm with Frank on this.  Nitrate is nitrate, regardless of whether its 
moving through or locally derived.  10 ppm is 10 ppm, and all else being 
equal it should have the same effect in either case.  I guess that in 
this case "all else" isn't equal.

In my tanks I suspect that iron or some trace element is more limiting to
plant and algae growth than any of the macro nutrients.  I think that
makes them distinctly different from natural settings.  And of course, my
tanks probably don't support more than a small part of the enormous
diversity of organisms that cycle nutrients in natural settings. 

> If a plant in my tank, and another in the river both have 10ppm of nitrate 
> in the water that they are touching, and if both are in sufficient current 
> that new, 10 ppm water is alays flowing over them, then why should it 
> matter if there is another billion gallons upstream or not?

It shouldn't.

In fact, I fail (miserably) to understand the logic of adding nitrate
fertilizer to limit algae growth. 

Roger Miller