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RE: Trickle Filters and CO2 Loss

> Date: Tue, 31 Dec 2002 13:38:59 +1100
> From: "Adam Shaw" <adams1 at comcen_com.au>
> Subject: Trickle Filters and CO2 Loss
> G'day all,
> I am setting up a 5x2x2 tank with a sump-based trickle filter system.
> am going to be running an external CO2 reactor with compressed CO2,
> powered by a small rio powerhead.
> I have read the article on aquatic concepts regarding co2 loss from
> trickle filter systems, and really it has left me wondering. I know
> many participants in the APD use trickle or wet/dry filter systems on
> their planted tanks.
> My question is this - what methods do you guys use to minimize co2
> from the trickle filter systems? I would rather not be re-filling my
> cylinder every other month...
> Thanks,
> Adam Shaw
> Australia

Aquatic Concepts is George Booth's site.  Hopefully George will respond
to this.  Nothing better than straight from the horse's mouth.  But just
in case he does not:

I recently had some off list discussion with him regarding under gravel
heaters (that I need to post a response to - sorry for my tardiness),
but I happened to ask essentially the same question.  About every
trickle filter I have seen has a provision to hook up an air stone in
the bio-media chamber.  My concern was about using an air stone in the
bio-media chamber thinking that it might not be good for CO2.  I figured
that if you were pumping air into the drip chamber the air has to go
somewhere, therefore you would have to have a hole in top of chamber
which might result in increased CO2 loss.  George said he does not use
the air stone.  He also said that they have a pretty good lid on the
chamber to prevent loss but it is not sealed - just covers the top.  I
believe he also runs his CO2 reactor in the sump.  I will try to find
the e-mail and copy the pertinent sections below.

Sections from 2 e-mails I sent George (GB):

> While I have your ear I have a question that has been bugging me for 
> some time.  Regarding filters, I have noticed in the Dupla book they 
> show a wet-dry trickle filter with aeration in the chamber with the 
> bio-balls.  Many of these filters I have seen have a provision for 
> this and many do not.  Do you aerate the filter?

Nope, that is one of the keys to NOT losing a lot of CO2 in a wet-dry
I conjecture that the media chamber quickly gets a high concentration of

CO2 from outgassing of the water with the air in the chamber reaching 
equilibrium with the CO2 in the water. If you aerate, it blows the CO2 
out of the chamber and you will lose a lot of CO2. We aerated at first 
then doubled CO2 tank life when we stopped. And then you don't 
get stupid air pump humming all the time. There is still lot's of fresh
being brought in along with the water flowing into the inlet. That's
what all the gurgling is about, right?   

> In some of these filters the top is fairly well sealed...

Except for the 2" diameter long hole (the inlet tube).

> I have never had a trickle filter up and running.  I take it from what

> you say that the overflow tube is not full of water and sufficient air

> goes down it to permit the bacteria growth (or whatever) on the 
> biomedia to make it work.

Exactly. Besides, even if bacterial growth is compromised, not much is
needed in a plant tank anyway. It's a nice place to put CO2 reactors and
such and is easier to keep clean than a canister filter. 

> I would also then assume that you have
> yours set up so that the top is fairly well sealed.  Correct?

We've done nothing special in the sump. The cover is not sealed, but it
covers the media chamber fairly well. It interlocks with the drip plate
to keep water in. I've done a bunch of stuff around the overflow box to
make it almost silent. Two of the tanks are in the TV room and a lot of
gurgling doesn't cut it. 

Hope this helps.