As some of you know, I've been experimenting with DIY CO2 in a 20H these last few months. For diffusion Ive had the raw CO2 line running into the intake of an Aquaclear HOB. The prop chops up the bubbles, which then have to flow up through the media before reaching the outflow.
Due to the Aquaclear's design, it is actually a more efficient version of the popular little Hagen filter mod - https://www.youtube.com/watch?v=liuXWQcJCcU
But I digress...What I discovered is that it makes a huge difference whether the line is running vertically or horizontally. Initially I had the line running straight up through the bottom, like you see here -
There was one big bubble at a time coming out. When it hit the propeller there was a distinct chirp sound. From the outflow came a small amount of very tiny bubbles, larger than mist size, but small enough, and few enough, to indicate that decent diffusion was taking place.
Just to tidy up the look of things, I decided to drill a hole in the intake pipe near the surface, and run the line in there instead of having it come up through the bottom. Like so -
This one change made a huge difference in what kind of bubbles came out of the line.
Instead of one big bubble at a time, there is now a steady stream of small bubbles, too many to count, in rapid succession. The change in position alone became it's own diffuser of sorts. No more chirping sounds. You can still hear it, but it's more like a very faint, steady hiss. Visible from the outflow now is a sparse, extremely fine mist, which I believe indicates a better rate of diffusion.
So anyway, I thought this might be useful for anyone using HOB filters, powerheads, etc to diffuse their DIY CO2.