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CO2 reactor from sponge filter

Hi all.

I was having lots of trouble with my DIY CO2 system.  I had hooked up the
CO2 to the input of my Eheim 2213.  Unfortunately, this turned out to
be noisy and frequently made my filter slow down to a crawl.  So, I decided
to build another type of reactor.  Basically, it's the same design as
the one Erik Olsen put on the Krib.  The only difference is that I made it
out of a Hagen sponge filter (you know, the one that is driven by an air
pump).  This is the kind that has a "T" bar at the end so that you can
put two sponges on it.

Here is a quick diagram of how I put it together:

         |----- Flexible tubing acts as an adapter to cannister filter output.
    ___ ___
   ( __|___
   | |
   | |
   | |  <--- "Output" of the sponge filter.  Now the water "input" of reactor.
   | |
   | |_
   | __  <--- "T" bar of the sponge filter.  Now the water "output" of reactor.
   | |
   | |   <--- Flexible tubing that acts as an adapter.
   | |
   | |   <--- Airline input of the filter.  Now upside down and plugged
   | |\       at the bottom.

The Eheim tubing from the filter output was too small to go over the input
of the reactor.  I added a small piece of flexible tubing (5/8" OD?) that
goes in the input to the reactor and the output to the filter to act as
an adapter.

There is a similar problem with the "T" bar and the airline input piece
(they don't go together).  I used a piece of the Eheim tubing (7/8" OD?)
as an adapter.

The airline input is placed upside down so that the bottom has room to
accomodate a plug (I didn't have anything appropriate so I jammed some
filter floss in there -- the pressure isn't high, so I think this will hold).

The CO2 goes into the airline input.

Finally, I filled the tube with aquarium pebbles (mine are probably too big
to be efficient, but it still works well).

After one day, I measure about 35 ppm CO2 (almost double the efficiency of
using the cannister filter as a reactor).  The CO2 bubbles in and slowly
bubbles out of the output of the reactor.  Thus, I'm sure this could be
made even more efficient.  However, I don't think it needs it :-).

Cost: ~$16 Cdn.  Advantages: No drilling, cementing, etc required.  Looks
really good.  You can convert it back to a sponge filter in emergencies.