re: Powerhead CO2 injection method

>From: Hardjono.Harjadi at Eng_Sun.COM (Hardjono Harjadi)
>Date: Mon, 4 Dec 1995 10:56:39 -0800
>Subject: Powerhead CO2 injection method.

>You can just hook up the airline that carries the CO2 into the venturi
>valve inlet. But the real trick is on the powerhead outlet. Use the
>outlet adapter (included with Aquaclear and Penguin) and connect
>plastic tubing to the outlet of the powerhead. Direct the output to the
>bottom of your tank. This way the CO2 has more time to dissolve into the
>water because of longer contact inside the plastic tubing and longer travel
>distance inside your tank before reaching the surface.
>I can drop the pH in my tank by 1-1.5 using this method with Alkalinity=3 dH

What I did was I placed a small overturned plastic can facing the powerhead 
outlet. The powerhead outlet is blowing upward and the CO2 get caught in the 
can. The turbulence caused the CO2 to dissolve quickly and other gasses escape 
through a small hole at the top of the plastic can. The distance of the can is 
about 2" from the outlet, so the back-pressure is not much.