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Re: nitrate


The question of where the nitrate comes from and why it builds up in the
tank are really different questions.

There is very little nitrogen fixation in most aquariums, so the nitrogen
in the nitrate must come from something you add to the tank.  That could
be the nitrogen in plants and fish that you add to the tank, but most
likely it's the nitrogen content in the fish food.  It could be from
fertilizers if you use them, but you say you don't.  Public water supplies
can carry almost 45 mg/l of nitrate without triggering regulatory action,
but you say your water tests nitrate-free.  Some could even originate from

I just went through the calculations to estimate how much fish food you
would need to feed to your tank to get 50 ppm of nitrate over a couple
months time (60 gallon tank w/30% weekly water changes), and it's more
than 9 grams of dry flake food or its equivalent per week.

If you're feeding that much, then the high nitrate levels just mean that
your plants aren't using much nitrate.  How about this as an alternative
explanation for the apparent rise in nitrate levels: your *old* test
kit lied.  You had substantial nitrate all along, and it's just not
dropped off yet.

I wrote a note to the list a few months back about results from the 3
different nitrate test kits I have.  The AP dry tab test kit really
doesn't perform well compared to other tests, so your test themselves
remain most suspect.

As to why nitrate might accumulate...

Nitrogen that you add to your tank in any way can go three ways:  it can
become biochemical nitrogen (proteins and nucleotides in living
organisms), it can be stable organic nitrogen mostly in the detritus, or
it can become nitrate. Labile organics, ammonia/ammonium and nitrite are
just intermediate compounds in the conversion of nitrogen from one state
to another.  Some setups may promote denitrification and in that case some
nitrogen may end up as nitrogen gas.

There are practical limits to the amount of nitrogen that can be stored in
the living organisms and detritus in a tank, so usually a lot of the
nitrogen we add to a tank ultimately gets converted to nitrate.  If you
don't remove it, then it just builds up.

That's why we do water changes, and 30% water changes weekly are more than
adequate for most purposes.  Even with water changes you will usually see
some nitrate accumulation unless you have some other process acting to
remove the nitrogen.

In a tank with a healthy population of fast-growing plants we have another
process removing the nitrogen.  The plants take up the nitrogen, then to
keep the plants down to a reasonable mass we trim and prune and remove
plant material.  When we do that we also remove the nitrogen that the
plant material contains.

I've heard it said over and over (for years) that dirty filters cause
nitrate buildups and honestly that can't be true; filters don't add
nitrogen to your tank they just help get it converted from one form to
another.  If a filter is regularly cleaned then some nitrogen is removed
along with the detritus and the biofilm that you wash out of the media; if
you don't clean it regularly, then that nitrogen doesn't get removed.  In
my experience the amount of nitrogen removed in regularly cleaning a
filter may be negligible and the difference between a dirty filter and a
regularly cleaned filter may be too small to detect.  The importance of
the filter will vary with the type and size of the filter and the activity
of the biological culture in the filter, so others may have different

> Well, someone else has mentioned off-list that it could be a nutrient
> imbalance that keeps the plants from utalizing the nitrate.

You mentioned just adding DIY CO2.  If in the past your plant growth was
slowed down because of low CO2 levels, then adding the CO2 may increase
plant growth and help control nitrate levels.

> This is the
> thing I, as a neophyte at this, am grappling with.  I have surfed The
> Krib till my eyeballs bleed.  I have wrestled with all the rest of the
> pages mentioned on this list.  I go to bed in the wee hours feeling like
> an utter idiot.  What method would I use to determine what is missing?
> Other than high nitrate, and one melted crypt, what would I be looking
> for to figure this out?  My lotus lillies are sending out one and a half
> huge leaves a day.  The cabomba piauhyensis was planted less than 2
> months ago, and its a forrest.  It seems like I am doing all the right
> things, but something unexpected always goes wrong while my back is
> turned, and it drives me crazy to not know the answer why.  Maybe its
> because I am convinced you all know exactly what you are
> doing....(snicker!)

It sounds to me like you're trying to argue with your own success.  As
long as things are working, then you may as well throw the nitrate test
kit away, stash the PMDD ingredients and just keep on doing what you're
doing now.

Oh, Crypts are real difficult to ID, but the plant you described with pink
stems and leaves and green veins could be C. walkeri.  You might look for
photos to see if that's what they look like.  I think there's some good
shots in Amano's second volume.

Roger Miller