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Re: Reducing diet

Dave Gomberg <gomberg at wcf_com> wrote:
> About 2 years ago I set up three 10 gallon seeding growout tanks.
> The substrate was 2mm gravel with laterite below.
> Since I had tanks, I put fish in them.  In one of the tanks I spawned H
> cristatus and raised the fry.  Eventually there were 24 2" cichlids in a 10
> gallon (over 1" per gallon I guess).
> I was running an Aquaclear mini.  Needless to say the fish made short work
> of any plants
> and devoured Tetramin like there was no tomorrow.   I was feeding about an
> ounce a week.
> The water was turning tinted so fast I was changing 30% every day or two.
> Finally in desperation (down to about 15 fish at this point) I tore down
> the tank.
> Where there had been laterite below the gravel, there was now a mixture of
> laterite
> and COMPLETELY REDUCED IRON.   It looked like tiny iron filings.
> I am pretty sure this black stuff was not a sulphur compound (tho it could
> have been FeS)
> because it was very dense.
> That says something about how anaerobic and what strong reducing conditions
> can exist
> in the gravel.
> Interesting, no?   Comments?  (Other than "don't do that!")

Yes. The term "anaerobic" really implies without oxygen or air. Redox
potential measures or indicates the presence of strong electron donating
molecules in the water mixed into the substrate. Under conditions where
organic material is decomposing, such as the abundant fish excrement,
the chemical chemical reactions can occur faster.

I think a test for the presence of iron in the black deposit might be to
heat it up to see if it forms a magnetic iron form. A spectrographic
analysis would also be conclusive. Does it form a rusty appearing oxide
if you expose it to air? It could be quite a mixture of things. I
suppose another possibility might be some kind of bacterial growth. I've
also noticed that certain parts of the substrate where there are organic
materials also darken. Other areas closer to the surface also get the
characteristic rusty orange color of iron stains where the iron oxide
comes out of solution. Rusty zones also occur around where roots touch
the glass side of the aquarium. It's kind of fascinating to marvel at
the mysteries of bio-chemical reactions; the interaction of microscopic
organisms and the complex mixture of soil and detritus while
contemplating a patch of oddly colored subsoil.

Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!