Re: Nutrients

[Paul Sears <psears at nrn1_NRCan.gc.ca>]

> From: Neil Frank <aquarian_subjects at mindspring.com>
> Subject: Re: nutrients
> 
> Aren't there other ways to lower the pH without adding CO2? For example,
> peat in the filter or substrate.

I think that that works by reducing the KH.

> We know that peat will reduce reduce
> hardness. Conceptually, it seems that this is due to the lowering of pH
> thru the release of organic acids. Then, it seems that the lower pH shifts
> the HCO3/CO2 equilibrium towards more CO2. [Please note that I am not a
> chemist, so I await comments from Paul].

The oddity of the CO2/bicarbonate system is that the acid (CO2) is
a gas and is free to come and go.  Its concentration in the water is
set only by the fish, plants, air, CO2 system, etc. and is _not_
dependent on the water chemistry.  Anything one does to alter the pH
by adding an acid or base can only have a transient effect on the
CO2 concentration.  Adding acid will convert some bicarbonate to
CO2, but the extra amount will leave over the next few hours, and
the concentration will end up right back where it started.  The KH
will be lower.  Conversely, adding (say) sodium hydroxide will cause
a temporary drop in the CO2 concentration as some is changed to
bicarbonate, but more will then come in from the air.  The KH will
now be higher.

>  I have a peat substrate tank that grew wonderful plants for over 5 years
> without injecting CO2. I assumed this primarily was from HCO3 conversion,

You would have to keep on adding bicarbonate and peat.  I think that
almost all of it would have come in in the ordinary way, from the air
and fish.  One could get an estimate of the total amount of CO2
from a given amount of peat by doing a titration, I suppose... :)

> in addition to supplemental CO2 from the slow decomposition of the OM.

Yes, but surely not all _that_ much of it disappeared over the years...?

> Because I have soft water, I had to be careful to not let my KH get too
> low.  When growth slowed after the first 5 years of relatively effortless
> success, I added pressurized CO2 and everything has been fine since
> (another 6 years).  Same substrate, albeit with less OM.
> 
> Neil
> PS. I also did water changes and added traces, etc. :-)

How much water did you change, how often, how much KH was in the
replacement water and at what pH did you operate?.  If you were
adding soft water (as implied above), I rather doubt that the total CO2
added this way can have been all that great.  Did you do KH measurements
on the operating tank?  I'd be interested to try to work a few things
out......

I've never used peat.  Does it reduce measured GH _and_ KH?

-- 

Paul Sears
psears_at_nrn1dotnrcan.gc.ca, 613-996-4171, facsimile / télécopieur 613-996-9400
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