From: oleg@Veritas.COM (Oleg Kiselev)
Newsgroups: rec.aquaria
Subject: Re: Biological Filtration
Date: 16 Apr 92 16:10:11 GMT
Reply-To: oleg@veritas.com (Oleg Kiselev)
Organization: Palo Alto Killifish Loft
X-Disclaimer: I speak for myself only unless explicitly indicated otherwise

This is getting long...

A recap:

Greg stated that his protein skimmer (FF from here on) significantly
lowered the nitrates level in his tank. (1)

I asked: (2)
>>>>how are you managing to decrease the nitrates level with a protein skimmer? 

Greg replied: (3)
>>>fish excrete ammonia into their environment,

... which is a true statement, but it has nothing to do with my
question.

I replied with: (4)
>> Skimmers do not do very much to directly remove ammonia. 

Greg answers: (5)
>I don't think that I said anything about ammonia...

Greg, FF can't remove nitrates directly.  Nitrates exist as ionic parts
of inorganic nitrate salts.  That's the final product of aerobic
nitrification.  The earliest inorganic stage of this process is
ammonia.  But FF does not remove ammonia either.

FF works by producing a myriad of bubbles which attract organic
molecules to their surface.  This creates the stable, lasting foam.
"Dry foam" is basically nothing but the organic scum bound together by
surface tension of the bubble.

Ammonia is, indeed, excreted by fish.  Ammonia is also the major result
of decomposition of organic stuff (fish crap, left-over food, decaying
plants, fish hormones and slime, etc.).  And that's exactly what FF removes
through foaming -- the "proteins" (and fats, and carbohydrates, and organic
acids, and pheromones, and whatnot).  If these proteins are not removed,
they are consumed and broken down by bacteria, infusoria and rotifers and
end up as ammonia.

Now, let's get back to quote (3), Greg.  This was your reply to my question
(2).  So you did say something about ammonia and it wasn't exactly clear to
me why.  

>Plus, these things are
>broken down from ammonia->nitrite->nitrate, not the other way around.

True, but not completely.  Anaerobic bacteria (Pseudomonas spp.) reduce
nitrate to nitrite and further to oxygen. if there is no oxygen next to
them and bacteria food (lactose, alcohol, whatever) is present.  Even
the "normal" aerobic bacteria do it if O2 levels are low enough.

>According to many books, the nitrate levels in most tanks go high and
>stay there because there are not enough real plants to handle the
>nitrates.

This is not quite true.  Most true aquatic *plants* (i.e. not algae) 
do poorly when the nitrates levels exceed 20-40 ppm, at least that's what
happens to freshwater plants.  As nitrate levels climb, plants need more and
more light to maintain the same level of photosynthesis.  At some point
(60ppm, I seem to recall reading) plants shut down.  Some plants do not mind
high nitrate levels: terrestrial plants can deal with them, water hyacynths
revel in them, Bacopa caroliniana will do just great.  But most aquatic
plants will not.  Unfortunately, too many aquarium books are full of myths 
and ill-researched assumptions.

>Many fish can live comfortably in levels of 110ppm+ of
>nitrates since these are far less toxic than ammonia or nitrites.

This is quite untrue.  There is a drammatic change in the fish behaviour
as nitrates levels go above 10-20 ppm.  At least in fresh water fish, which
are supposed to be far less sensitive to water chemistry than salt water
fish, high nitrates levels cause fish to be skittish and jumpy, become
prone to diseases, and in general not a good thing to do to the fish.
Reef inverts will die long before that.  

So yes, you can reduce your nitrates by using FF, but keep in mind that 
FF does it by removing ammonia sources before they become ammonia rather
than dealing directly with ammonia, nitrites and nitrates.
-- 
"... i heard the droning / in the shrine
	     of the sea-monkey / palace of the brine ..." -- Pixies.
Oleg Kiselev                                             oleg@veritas.com
VERITAS Software                           ...!{apple|uunet}!veritas!oleg
Newsgroups: rec.aquaria