Re: [APD] Diffusing CO2

["S. Hieber" <shieber at yahoo_com>]

--- RMGTBTS at aol_com wrote:

> Question 1. Has anyone experienced problems with running
> their CO2  through 
> their canister filter? i.e. having the motor burn up
> because of a loss  of 
> siphon I guess due to a gas blockage?

So long as gas does not collect too quickly inside the
filter, it should be able to push out the gas -- burping
every now and then, so to speak. As a canister filter runs,
its media collects detritus and grows biofilm which
gradually impedes the flow of water through the media. When
it becomes substantially impeded, it's harder for gas to
remain disolved in the water and gas will more easily
collect in the filter.

If you are running about 250-300 bubbles per minute, you
might be injecting the gas faster than it can be absorbed
into the water and faster than the filter can discharge the
excess -=- especially once once the filter media begins to
load up. If things are working fine now, then be sure to
keep an eye on the filter flow rate -- when it slows down,
rinse or replace the media.

The filter motor shouldn't be damaged unless it is running
dry or without a more or less continuous flow of water over
it. Usually, if the rotor is running dry, the rotor will
clatter. The replaceable bearings on the rotor should
"burn" and go bad long before the motor coils overheat
enough to short and ruin the motor. In fact, the motor
probably can't heat up enough to damage the couls unless
the rotor is not turning at all.

> i have been advised that with the water conditions in
> Milton MA coming out  
> of the tap at KH<1 GH<1 pH 9.0 to 9.4 (BTW i verified
> this with a chemist  at 
> the water department and was told they add Sodium
> Carbonate (not  bicarbonate) 
> to raise pH above 9 to reduce risk of old lead pipes in
> some of the  older 
> homes leaching out lead) that I might need to run 4 to 5
> bubbles/sec  on the CO2. 


Oy Gevalt! I would have expected more "hardness" with such
a high pH, especially if a carbonate is being added to the
water. Are you sure about the KH & GH numbers?

> When I did this I had an Eheim Professional 2 motor
> burnout (unit  < 2 years 
> old). A few months later I had the occasion to pick up a
> Fluval 204  at a low 
> cost and decided to just try again. After two weeks
> everything is fine  with 
> the filter and I have noticed that there are NO Visable
> Bubbles coming out  of 
> the exhaust line. Before, the diffuser I was using had a
> pretty good  
> discharge of visible gas going to the top. Wasted gas?

You are using a CO2 diffuser *and* injecting into a
canister. What kind of diffuser and is it located before
the filter intake or after the filter output? Or did you
mean the filter outlet pipe? If CO2 bubbles are steadily
coming out the filter outlet pipe, then you are almost
surely injecting the CO2 faster than it can be absorbed --
i.e., too fast for the rate to be doing you much good.

Occassional bubbles, not so bad, but steady bubbles, then
the CO2 is probably overcranked, i.e., sped up beyond a
useful rate.

  
> Question 2. Wouldn't the efficiency of the diffusion
> significantly affect  
> the needed rate of injection?

Well if more of the CO2 is dissolving into the water, then
there is less wasted gas and you don't need to use as much,
other things being equal. If you have significant surface
turbulence, that will case the water to shed the CO2
quickly. That can be as important as the efficiency of the
diffuser. See if there are ways to conserve the CO2 once it
gets into the water. Then, if you are still injecting at
250-300 bubbles per minute, consider using an external
reactor instead of the canister as the CO at -water mixing
chamber. You can make one inexpensively like this:

http://www.aquaticscape.com/articles/co2reactor.htm

Connect it in-line with either the output or input of the
canister filter with the water going in the top of the
reactor and you should be able to get 100% absorbtion.

Btw, what size aquarium is this that requires 300 bubbles
per minute?

Good luck, good fun,
Scott H.
 


=====
--- Christel Kassellman is returning to America! ---
The Northeast Council of Aquarium Societies will feature Christel, author of _Aquarium Plants_, among its speakers at its 30th Annual Convention. It's the longest running consecutive general tropical fish convention in the country and one of the most fun to attend. 

March 18-20, 2005
Marriott Hotel, Farmington, CT
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