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Re: [APD] Re: CO2 reactor help

--- Clint Brearley <clint_brearley at telstra_com> wrote:
> Scott H. wrote:
> > Imo, if you are feeding CO2 into your canister, yu
> don't
> > need another reactor, the canister is serving that
> purpose.
> This contradicts what you wrote in a previous post dated
> Wed, 10 Sep 2003 03:40:16 -0700 (PDT): 
> > Before you fiddle around a lot with your filter and
> media,
> > you might want to consider making an external reactor. 
> If
> > you have a source for PVC pipe, they're easy to
> construct
> > and inexpensive.
> You inspired me to build the reactor in the first place
> and now you say I don't need it? I think it would be
> better to have one, especially as I will shortly be
> replacing my yeast CO2 with compressed CO2 and plan to
> use higher bubble rates than I'm getting from the yeast.

Sorry for the confusion. If there was just one way to do
things, I might sound more single-minded.

I still stand by my opinion that external reactors are the
best way to go.  A canister filter is, in a way, one kind
of external reactor but not my favorite, just the cheapest
since one probably has the canister already. But most
canisters output from the top and that's a significant diff
from your basic external reactor.

External reactors are very simple devices, essentially just
a box (or cylinder if you prefer) where water and gas can
mix.  That's where *I* want to feed the gas.  So long as
there is some water at the bottom of the box (cylinder) so
that gas bubbles can't be carried out by water flow, the
reactor should give you 100% absorbtion.

My experience with canister filters as reactors is that
they don't give 100% absorbtion because, at least in part,
the outlet is at the top where gas can collect then burb
out.  With your basic external reactor, that can't happen
since the outlet is at the bottom.  Some gas will collect
but it won't keep collecting more and more, even without
burping, unless the water flow is way too slow for the CO2
flow rate.

If you're feeding into the canister intake, then flowing
through the CO2 reactor, then the canister itself, I guess
the point is to have the CO2 flow up the intake to the
reactor, then collect (be trapped) in the reactor until it
dissolves.  Not a bad technique.

My suggestion was that you try the simpler cheaper
alternative first and if that worked acceptably to you,
then keep things simple.

> > Since you have the reactor, you might try putting a
> > separate powerhead or pump on it and fee the the CO@
> into
> > that water line or directly into the reactor.  You
> should
> > end up with 100% absorbtion.

The thinking here was that, in your situation, you needed a
higher water flow through the reactor.

I have to admit that I have little experience using an
external reactor on the intake side of a canister setup.  I
know the arguments for it being preferable to being on the
output side, but they just don't work in my brain --
perhaps, more's the pity for my brain ;-)

On my 30 gallon tank I have a 2" by about 12" cylinder
external reactor fed by a micro-powerhead that's rated for
about 80 gph or something like that and probably pushes
about 40 gph after it's been in use for a while and some
biofilm collects on the rotor and the tubing to and from
the reactor.  The CO2 feeds directly to the intake on the
powerhead (a la Tom Barr) and powerhead pushes the water
and CO2 into the reactor.  That keeps the aquarium at 20-30
ppm CO2 and the CO2 tank lasts for many many months -- (you
wouldn't believe how many).  The CO2 feed rate is very slow
and there the build up of gases in the reactor is never
more than about 1/4 - 1/2".  It's a closed aquarium without
surface turbulence.  If the tank was open or had surface
turbulence, the CO2 flow rate would need to be much higher
and then, the water flow rate might need to be higher.  In
that case, if the CO2 and water flow rates still allowed
gas build up then a larger reactor would be needed -- but
that's not likely on the 30 gallon unless I start having
ways to shed CO2 from the aquarium very quickly -- say, I
added a wet/dry or a few biowheels or an airstone.

On my 150 gallon, I have a 3" by about 14" reactor and a
water flow rate of about 150-200 gph - it's fed off of the
manifold from the QuietOne pump (the old version) on the
wet/dry sump.  Even though it's a closed tank (glass
covered), the CO2 rate is much much higher than on the 30
-- about twice now what it was when I had a sanister
instead of the wet/dry onthe aquarium. But the collection
of gas at the top of the reactor never gets to be more than
about 1/2 - 1 ".  In fact, I can use the size of the gas
collection at the top of the reactor as an ersatz
measurement of the CO2 level in the aquarium.  If there is
no visible gas collecting, the CO2 level is generally less
than 20 ppm.  At about 1/2", it's about 20 ppm. At 1", it's
about 30ppm.  This will differ from set up to set up and is
only an ersatz measurement, like counting CO2 bubbles.

If I drain the reactor -- say I remove it for cleaning or
soemthing, and then reinstall it -- then it collects a
small amount of water at the bottom very quickly but
doesn't "fill" with water for about about a day.  It slowly
fills until the gas at the top is about 1/2- 1". I don't
mind that it takes that long because no CO2 escapes during
this time. The higher the water flow rate, the faster it

When I had a canister on the 150g instead of a wet/dry, the
reactor behaved much the same way although the water flow
rate was higher (closer to 200-300 gph) being fed from the
canister.  An "empty" reactor would fill more quickly at
that higher flow rate.

> I've got a couple of spare powerheads lying around, so if
> the priming doesn't work and I can't find any other
> solution, I may give a powerhead a go at driving it.

You might also try putting the reactor on the output side
of the filter -- the reactor may be more likely to fill
with water -- I don't think so, but it should be relatively
simple to try ;-) .

Sorry for the ambivalence or confusion or whatever you want
to call it. But just to be clear(er?), I think external
reactors are the best way to add CO2 and I don't think I
would do it any other way on my own aquaria.  Of course,
aquatic gardeners differ in their preferences and much
better gardeners than I do lots of things differently than
I, differently than each other.

Scott H., who never contradicts himself, except sometimes.

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