The sand filter in the designs mentioned ARE touchy! Flow is critical! Too much, and your sand flows right out, too little, and it doesn't go into a fluidized state. I placed the sand filter at the end of my flow loop, but solids wouldn't matter in it as there are no dead water areas to create any anoxic condition, and solids will either decay, or flow through.
FWIW, the media used is not regular sand. It is an angular material that is close to neutral buoyancy for easier fluidization, larger, uniform surface area and better cleaning when bouncing around in the fluidized state.
If I were going to design my own, I would make it conical in shape so that the upflow is so minor at the wide top, sand flowing out would not be an issue.
I just liked the sand filters because the surface area and self cleaning couldn't be matched in the same space/flow used. The media you use, Cecil, is good from what I have read, but to get the same surface area, you would probably need at least 100 times the space as the sand, plus, the inside parts could clog fairly easily, potentially creating the anoxic areas you mention.
Interesting. Yeah you can't match the surface area of sand or sand like material. What is this angular material you speak of? I know size of the grains is very important and even with the best of care you loose sand over time and need to replenish it.
Inside parts of MB3 DO NOT clog easily. They are constantly rubbing up against each other and the openings inside are fairly large. The media changes color over the years but no clogging. They are not as fine as Kaldnes which will clog over time.
