| Shaw,
Welcome to the board! Glad you've decided to post.
Most media hosts the thickest colonies nearest the source of air and food. In a down flow it's on the top of your media and on an upflow it's on the bottom.
The kind of bacteria can also be affected by the natural UV present in light especially where the downflow is used.
The deeper the media the more it affects the flow and the availability of food and air.To take advantage.
I have 3 vortexes in series, 16 inch media, all up flow and all with an airpump for each individual vortex. I started with air stones on top to re-introduce air into the next chamber. I then , after 2 years switched the airstones underneath the media. The results were markedly better with the later. I thought all that heavy air would blow all the food and water by too fast.
Don't know the theory but can tell you what works in practice. I'm not gonna change my system but if i was doing a new one I wouldn't hesitate to go ten inches for media depth. I've spent time with Peter and have an enormous respect for his knowledge. It's what he runs at his home pond. I know he's been working with EA and k-i but don't believe he's changed over yet or any time soon. BTW this concept came from Sakai-san of isawa. If you ever get a chance to read up on the man and his story you should do it. |