[GpsFrontier]

The floating problem is solved with this kind of light weight medium by simply moisten it well, prior to run the system. If wet it doesn't float or go anywhere.

I always pre-soak and wash my medium before placing it into my systems. I just figured everyone else would also and that would just be a given. Wet wood does float, depending on the type of wood some will float more than others. Hard woods usually sink first, but pine is considered a soft wood. Just soak it in water for a few days to see how much still remains buoyant. But regardless like I mentioned before, as long as the water level is not to high allowing the bottom portion to become buoyant, and the cycle times are long enough to keep the wood saturated with moisture one or two inches below the top of the medium, I don't see any problems with using it.

As the plants get older and the root systems get more extensive there will be less chance of any problems with any dislodging or shifting, it will become a solid mass of roots by then. I would just be mostly concerned while the plants are still small. You should design the overflow for a flood and drain system to be easily adjustable no matter what growing medium you use. That way you can test things at different levels to see what works the best for the plants you are growing.

The sawdust or mix get filled in porous (woven) poly planting bags (of adequate size) first. Then you actually close the bag, turn it or lay it flat, pinch or cut a hole(s) in the bag and transplant your seedling through the slit in the medium. Then you simply drip (often a pin dripper is sticked in the bag) and let go to waste, evaporation actually.

Ya, this is called a "Non Recovery drip system." Just for fun I attached a couple of images using this technique. The vertical bags are feed by the upside down water bottles at the top of the bags. These bottles are hand filled when needed, and have a slow dipper nozzle. The horizontal bags with the tomato's are fed the same way as a regular drip system. Also I think the tomato's in the bails of hay that I posted before a non recovery system, though you could run a channel underneath to recover the run off.

Has any one ever tried using Charcoal as the growing medium in Hydroponics?

I have never herd of using charcoal in hydroponics myself. I don't think you can ever get rid of the black residue. Simply because it's basically just a lump carbon that is the black residue. The hard wood charcoal would hold up the best I would think. I'm not sure what type of charcoal it is they use in filtration systems, I do know it's a special charcoal that's extremely porous. I'm not sure why it doesn't dissolve the same way as regular charcoal though. But if you can get charcoal that dosen't dissolve in water, leaving behind the residue that would clog your pump, it might work. I'm not sure what it would do to the pH, and if it would somehow filter out the nutrients from the solution. Nothing like a small scale system to test it in, just to see what would happen for s**** and giggles.