CO2 reactors

> From: Stephen.Pushak at hcsd_hac.com (Stephen Pushak)
> Date: Thu, 27 Apr 95 13:06:43 PDT
> Subject: Re: Flowering Aponogeton rigidifolius
> > From: trigg at jane_cs.waikato.ac.nz
> > Date: Thu, 27 Apr 95 11:16:17
> > Subject: Flowering Aponogeton rigidifolius
> > 
> > I'm not sure whether to be happy or jealous, but the A.rigidifolius

I forgot to put in a :-) when I wrote this ^^^

> > in my wifes tank has just started flowering, while the one in my
> > tank is having difficulty keeping ahead of the red-death-hair algae.
> > <snip>
> > There is no algae in this tank (although the water has just
> > gone a bit green in the last few days).

> The green algae is one of the first to colonize a tank and will inhibit other
> algaes. You can remove it with a diatom filter.

A friend of mine has a diatom filter so I'll give it a go.  We'll also
try to partially shield the tank from the windows.

> > My guess is the pH that's making the difference, so I've
> > been doing largeish rainwater changes the last couple of times, but
> > the pH is still around 7.2 at the moment. 

> Yes, pH is a large factor in what kinds of algae will grow. The question is why
> does your tank have high pH when you are injecting Co2? Perhaps the problem
> is carbonates in the gravel or decorative stones. 

"Independent tests" :) have shown the gravel is OK.

I would say the CO2 injection only brings the pH down by about
0.2 - I haven't figured out a system for efficient diffusion yet,
and it's a reasonably big tank.  At the moment I have 2x2l coke
bottles (of which I make one new mixture each week) bubbling into
one of the power filters.  The CO2 pretty much comes straight out
in tiny bubbles, so it doesn't stay in contact with the water for
that long.

I'm wondering if it's possible to have a reactor that will keep
the CO2 in contact with the water for a long time, but which
doesn't get "contaminated" by other gasses over time, maybe by
purging itself once it's not diffusing efficiently enough.  The
process as I understand it is as follows (feel free to correct):

You start off with an efficient reactor (say) half full of pure
CO2, with aquarium water running though it.  CO2 diffuses into
the tank water, and at the same time, oxygen and other gasses
diffuse from the aquarium water into the reactor.  Because the
relative concentration of CO2 has decreased, the efficiency of
the reactor goes down.  The reactor gradually fills to capacity
where it where it continues to operate at some (non-optimal)
level, with the occasional burble of CO2/other gas escaping
to the surface.

On the couple of reactors I've seen operating this _seems_ to be
the case, but I'm interested to know whether Erik or someone with
a similar reactor can confirm or deny.

A reactor that somehow minimized this "contamination" would
need a smaller reactor volume, and would waste less CO2.  The
question is, is it possible, and is it even worth worrying
about :-)

 Len Trigg ===================================================
 Comp Sci Grad   DoD#1334   trigg at cs_waikato.ac.nz             
 Waikato Uni     GPX250     http://www.cs.waikato.ac.nz/~trigg          
 GCS  d---(+) p c++ !l u+ e++ m* s n@ h--- f* !g w t++ r y+(*)