I purchased the Boyu CD-01 Diffuser on January 11th, 2010 and they arrived from Hong Kong on 01/23/10. The packaging was adequate; basically a standard padded mailing envelope that contained the two boxed diffusers.
It is a diffuser and can it can be attached externally either to the input or output tubing of a canister filter. The unit can also be used internally in the aquarium as well. There is a picture on the box showing the unit replacing the strainer on the input tube of a canister filter. It may be able to replace the strainer of an HOB filter, I have not tried that configuration yet but the end does fit into the strainer tube of an Aquaclear 50 HOB filter, so it would probably work.
Each diffuser measured about 5 ½ inches long by 1 ½ in diameter. The pictures below show the diffuser with the strainer basket in place for use internally in the aquarium attached to the input of a canister or HOB (hang on back) filter.
Here is a picture of the unit with the stainer basket removed for use on the input or output of a canister filter showing the overall unit length to be about 5 inches.
This unit is a diffuser and as such generates fine bubbles of CO2. It is not a reactor, which typically dissolves most of the CO2 generated, releasing few bubbles into the aquarium. In the picture below you can see how I attached my CO2 line with a check valve and where I cut the output line of my canister filter and installed the Boyu diffuser with wire ties. The CO2 enters the unit on the outside of the ceramic cylinder (the side you can see) and diffuses through the cylinder into the water that passes through the center. The are no obstructions so the flow of my filter is not drastically effected.
After two years of trouble free operation I can tell you that I really like
the Boyu CD-01 External CO2 Diffuser that I have been using. In fact I
installed another one on my second tank today. I have found the diffuser to
be trouble-free and easy to clean (I just run my 5' bristle brush through
the diffuser when I clean the canister filter tubing. In fact, I have only
had to clean my diffuser twice in two years!
Keep in mind that this is a diffuser and not a reactor, so I do get some
small CO2 bubbles expelled from the output of my filter into the aquarium,
but the amount is very minimal and they dissipate almost immediately.
I have not been able to find them online recently, they are manufactured in
China. I have included a link to video
I did of the diffuser in operation, sorry one of my first attempts.
5' Tube Cleaning Brush