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Re: Dennerle philosophy.


I'll take a shot at this...

> >
> >    Some eighteen months ago I received some booklets issued by Dennerle
> >which appear to provide additional information on Dennerle philosphy.
> >Quoting from their booklet "Algae problems? We solved them long ago"
> >

Yeah, right.

> >    " ... alga love an oxidising environment, they develop particularly
> >well and produce more and more oxygen, far too much for the fish to
> >consume in such large quatities.

The first sentence is the key assertion in this whole story, and unless
something important is left out then it is an unsupported assertion.  I
can accept that algae (or plants) can and often do produce much more
oxygen than the respiring critters will consume, but I see no evidence
that this favors algae.

> >    Algae quickly succeed in raising the oxygen level to 20-30 mg/l.
> >Contrary to popular opinion, such high levels are unnatural for fish;
> >for most aquarium fish the oxygen level of their natural habitat is only
> >2-3 mg/l.

These are some pretty extreme numbers.  20-30 mg/l of oxygen?  Maybe, but
I've seen lots of analyses from algae-laden water bodies and I don't
recall seeing many numbers over 12 mg/l.  Certainly not in an aquarium.
The supersaturated levels would be unnatural and probably quite
unhealthy for fish, but I don't know that their natural habitats would
normally carry only 2-3 mg/l.  I think most fish (those not specifically
adapted to low oxygen levels) are stressed at about 4 mg/l.

> >    Excessive amounts of oxygen will quickly destroy natural chelates:
> >the water will become more "aggressive".  The excessively high oxygen
> >content destroys the essential vitamins and renders the trace elements
> >inactive.  Plants, as well as fish, will then suffer from trace element
> >and vitamin deficiencies.

Ok.  I suspect this is true, but that it's true when oxygen levels are
"normal".  There would be a large number of other factors involved, and I
doubt that oxygen at supersaturated concentrations will control the rate
of breakdown of the chelates, coenzymes, etc. Of course they *might* have
evidence to the contrary.

> >   Because the conditions are ideal for algae, they will displace the
> >aquatic plants more and more.  Little by little, the plants will die as
> >a result of such unfavourable living conditions."
> >

This relates back to the original, unsupported assertion that algae thrive
in highly oxygenated environments.  It seems to me that if Dennerle is
right about high oxygen breaking down chelates and vitamins then this
would favor rooted plants over algae or floating plants; the algae are
totally dependent on the nutrients in the water column and it's those
nutrients that would be destroyed by oxidizing conditions, while the
rooted plants have additional nutrient sources in the substrate and should
be less effected by the oxidation and loss of nutrients in the water

> >Dennerle advocate regular measurement of oxygen.  The remedy for excess
> >(not sure what Dennerle considers excessive) is to reduce the lighting
> >period(s).
> >
> >Comments anyone?
> >--
> >Ernest G Austin
> >

Maybe you can tell that I'm not convinced.

I subscribe to the notion that algae growth is controlled by making sure
that one or more of the essential nutrients is deficient in the water
column, but available in the substrate.  That provides rooted plants with
a trememdous competitive advantage over algae.

Roger Miller