Minh,

Thanks for the links. I finally got around to reading.

I guess I'm guilty of doing what I hate: repeating mantras heard over and over again in the industry, that may or may not be well founded.

As most know, I'm a molecular biologist by education - I should know better.

I do know that, based upon my experience with sand fine beds, that once you get under the first about 3/4", they quickly become anaerobic.