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re:DIY CO2

This is what I do:

>I'm building my first home-made yeast CO2 injector, and have a couple of 
>questions that I'd appreciate your advice on:
>1) Does the bottle have to be above the aquarium?

Mine sits under the aquarium.

>2) Would a check valve help if it were to be paced below the

I don't use one. I found it tends to block the CO2 flow, resulting 
in infrequent but large bubbles. And why one is necessary anyway ?
Pressure inside the CO2 bottle is larger than at the aquarium end
of the airline (otherwise CO2 wouldn't flow at all). If pressure drops
at the end of CO2 production, water may flow back from the tank, but 
the empty volume in the bottle is barely one cup worth. And then the 
brew cannot flow into the tank because the pressure is gone. The only
risk is if the bottle breaks, or the airline disconnects. If the bottle
is well protected under the aquarium stand, how that would happen by
itself ? My cats don't go in there either...

>3) Should the bottle be placed upright or on its side?

Upright, and leave about 20% of the volume empty so to avoid the 
nasty brew from flowing into the tank if it foams.

>4) I'm planning to vent the CO2 into the intake of a Fluval 403 canister
>filter. What is the best way to do this? E.g., stuff the airline tubing
>directly into the side of the intake, add a disposable air stone and let the
>CO2 bubble up into the intake from below?

I have a Fluval 303 and didn't adopt that approach. I read in the archive
that Fluvals are sensitive to gas bubbles trapped in the impeller
chamber. They get noisy them. My experience with eventual air bubbles
caught in the chamber during maintenance tell me otherwise, but better safe
than sorry. So I built a cheapo counter-flow DIY CO2 reactor connected to 
the filter output via a diveter tee. It doubles as a bubble counter. Btw,
how you would measure the bubble rate if the airline end is stuck into the
filter input ?

-Ivo Busko
 Baltimore, MD