Re: CO2 diffusion and Fluval filters

>From: rrs0062 at ibm_net (Mark A. Thompson)

>This leads right into a question I was going to ask.  I've been trying to
>decide how I want to diffuse CO2.  I had originally planned to build a
>diffusor and hook it inline with my Fluval 403.  Then I thought it might work
>to simply run the CO2 into the intake hose of the filter, and let the filter
>do the diffusing.  The impeller in the Fluval is at the end of the water path,
>not the beginning.  That is, the impeller "pulls" the water through the filter
>instead of pushing it.  The result would be that the CO2 bubbles would never
>come in contact with the impeller (not a bad thing in itself) and would be
>trapped by filter media.  A friend of mine expressed concern that since the CO2
>bubbles wouldn't be broken-up, they wouldn't dissolve fast enough and a large
>CO2 bubble would form inside the filter.  Anyone have any thoughts about this
>or actually tried it with a Fluval?  Any help appreciated.

Yes, I have used a Fluval for this purpose (but mine is a Fluval 303).
Fluvals tend to have a problem with being fed CO2.  Not all CO2 is trapped
and dissolves in the filter media, especially when your CO2 injection rate
is high, and eventually it accumulates around the impeller and makes a lot
of noise, sometime cutting off the water flow completely.  I tried breaking
up the CO2 into fine bubbles with an airstone (just place the airstone
directly underneath the Fluval intake) and it helped quite a bit (in that in
worked much longer before starting to make noise).  I understand that Eheim
canister filters can "burb" themselves much better than Fluvals, and do not
suffer this problem.  

But as long as your CO2 injection rate is low and you break up the CO2 with
an airstone first, it should work.  I ended up with a homemade CO2 bell
instead though.