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Re: Aquatic Plants Digest V6 #66


Thanks for the response.

In addition to:

1)   HCO3-  +  H+  ->  H2O  +  CO2 (leaves)

I understood that I also have:

2)   4 NO3 + 3 S = 2 N2 + 3 SO4

Is that your belief also (that's supposed to be the point of it after

If so, is (2) a necessary requirement for (1) to occur (i.e. are bacteria
using energy from (2) to enable (1) to occur - so KH erosion should be
proportional to Nitrate removal)?

Is it likely that other xxx'ates are also consumed (Phosphates for

To be honest, using the denitrator is mainly out of curiosity to see what
happens rather than a determined attempt to control Nitrates.

Maybe all I've done is swap a Nitrate problem for a slightly smaller
Sulphate (& KH) problem!

Regards, Kevin

> From: Kevin.Buckley at uk_neceur.com
> Subject: Re: Denitrator question (freshwater) - CO2 & plants
> In case anyone's interested ...
> The denitrator was producing 0ppm NO3 outflow from 40ppm input within 48
> hours at about 200ml / hour.
> Within 3 weeks it was processing NO3 at a flow rate of 1 litre/hour &
> Nitrates have remained at zero.
> It's completely trouble-free so far (& seemingly insensitive to flow rate
> at the low levels I'm using) except that it seems to also be reducing the
> KH of the tank at a rate of around 1 degree / week.
> I've compensated for that twice now (raising the KH from 2 degrees back
> 4 degrees) but it's still happening - yesterday it was back down to 3.
> The outflow KH is the same as the inflow KH though, as is the pH, (within
> the limits of home testing) so it's clearly a very gradual process.

           At a reduction of 1KH/week, I wouldn't expect a measurable
between the intake and outlet.

> Happy New Year everyone!
> Someone bought me a denitrator for Christmas &, as a gadget freak with
> mains water already high in Nitrates, I thought I'd give it a go (Sulphur
> based, made by Deltec - see
> http://www.ultimateaquatics.co.uk/acatalog/Deltec_Equipment.html for a
> picture).


> - - I read somewhere that the outflow is quite acidic & that the reason
> because one of the reaction components is xxSO4;

           I looked at the web site, and I wouldn't be at all surprised if
the bacteria are making sulphuric acid, if they are using sulphur.

> - - Is that because it forms H2SO4 (or some other acid - is H2SO4 a
> acid BTW?)?

           It is.  The strong acid would then destroy the KH:

           HCO3-  +  H+  ->  H2O  +  CO2 (leaves)

> - - If the above is true (or even if it's not) how will this affect my
> ability to calculate my CO2 content using the KH / pH formula?

           Not at all.  There is no problem provided there are no other
_weak_ acids around.

> Mainswater is 30ppm NO3, GH=16, KH=5;
> Water change is just using mains water when the tank Nitrates start to
> too high (remember, they start at 30ppm!).

           I would just do lots of water changes if the NO3- concentration
tends to rise.  I don't think 30 ppm will
present a great problem, and if the plants grow well and the fish load
isn't too high, it will fall with time, not build up.  In that case,
to keep NO3- down, one _avoids_ water changes!


Paul Sears
psears_at_nrn1.nrcan.gc.ca, 613-996-4171, facsimile / tÚlÚcopieur
Natural Resources Canada, 1, Haanel Drive, Nepean, Ontario K1A 1M1
Ressources naturelles Canada, 1, Haanel Drive, Nepean, Ontario K1A 1M1
Government of Canada / Gouvernement du Canada