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Fun with power tools
For some time now I have provided CO2 to my tanks by feeding
yeast-generated CO2 into the inlet of power heads. The power heads do a
fine job of breaking up the bubbles. In the small tanks where there's not
much distance between the powerhead outlet and the water surface there's
no evident problem.
In my larger tank, where the powerhead outlet is directed through a spray
bar of sorts pointed at a slight downward angle, there is a problem. The
tiny bubbles coming from the power head don't dissolve, and they create a
cloud of bubbles all over the tank. The problem is especially bad in the
evening when the plants are really bubbling. I think what happens is that
when the incoming CO2 hits the pump, the pump not only smashes up the
bubble, but low pressures inside the pump also promotes rapid exsolution
of nitrogen and oxygen from the water into the CO2 bubbles, which keeps
them from dissolving completely. The same thing probably happens in the
other tanks, but in those cases, the bubbles hit the surface fast enough
that I don't notice a problem.
Here's where the power tools come in. I built a simple CO2 reactor to fix
the problem. I don't know that there's anything special about the reactor
-- there might be a half dozen similar designs out there -- but this one
worked pretty well so I thought I'd describe it.
The idea is to create a strong vortex inside a small length of pipe, and
to bubble CO2 into the middle of the vortex. Being light, the CO2 bubbles
tend to stay in the middle of the vortex until they dissolve.
It consists of a length (I used about 9 inches) of 1 1/2" schedule 40 PVC,
capped at each end, an inlet in the side of the pipe near one end and an
outlet in the side of the pipe at the other end, both arranged so that the
flow through the inlet or outlet is tangent to the inside surface of the
The end caps are standard PVC fittings, cut down so that they seat firmly
against the end of the pipe with only about 1/2" of overlap on the side of
the pipe. I drilled a small hole in one end cap and friction-fit a small
length of rigid plastic airline into the hole. The CO2 feeds into that
line. The inlets and outlets are tubing barbs cut from a 1/2" PVC elbow.
All of the PVC parts glue together with PVC cement.
The main problem is to get holes drilled into the pipe that are large
enough to fit the tubing barbs, and at a very low angle to the inside wall
of the pipe so that there is minimal impact between inflowing and
outflowing water and the side of the pipe. Once the tubing barbs are
glued into place the projections inside the pipe need to be cut down so
the inner wall of the pipe is smooth. Dremel tools are great for this
The whole layout looks something like this from the side:
inlet _) |
| S |
| w |
| i |
| r |
| l |_
and from the top, like this:
* 0 *
* CO2 in *
The reactor needs to be mounted vertically with a powerhead connected to
the inlet, and a CO2 line connected to the CO2 inlet. Both inlets are at
the top and the outlet is at the bottom.
The first one I made just as shown and set up to use inside the aquarium.
It works very well, but it's fairly obvious inside the tank. I'm making
the second one to hang outside the tank. It differs from this design
mostly in that the joints are all sealed with silicon.
The parts cost a couple dollars. It took about an hour to cut the pieces,
grind the ends smooth and square and to fit all the pieces. It wouldn't
take much time at all if (unlike me) you actually cut all the parts square
to start with. Curing the glue takes a little longer.
If the flow through the pipe is too fast, or not tangent to the side of
the pipe at the inlet and outlet then you won't get a good vortex inside
the pipe and CO2 will just flush through without much time to dissolve.
The longer the pipe, the longer the gas will have to dissolve.
Similarly, a larger diameter pipe should provide the gas longer to
dissolve and might accomodate higher flow rates. Also, the inlet and
outlet can be directed off in different directions. For internal
installations it might be better to have them at 90 degrees to each other.
In an external installation it might be better to have them at 180 degrees
to each other.
P.S. I managed to get one of the plecos out by putting a piece of
zucchini inside a pint jar and leaving it over night. The little guy was
feeding on the zucchini when I got up in the morning. I grabbed the jar
and moved him to another tank. One down, one to go.