Ive seen tables filled to the rim with hydroton and other mediums like flytocel and perlite,the reason people do this is for root mass,having roots exposed to light prunes the roots.
The problem with a table full of medium is that it ad's drastically to humidity levels,not to mention being the main culprit of powdery mildew which will topple even the best flood table.
Ive gave up on using any medium at all,i cover all my tables with 5ml panda plastic and cut precise holes in the cover to set the net pots in,this leaves the top of the net pot exposed to the light,to stop the light penetrating the top of the net pot i cut squares out of the panda and cover the net pot top,i also use an extension on the flood port and set the table at dead level so the gutter channels at the bottom retain water.
Ya get massive root mass without using any medium at all,ya just have to compensate for the lack of medium with increased flood times,if you can keep everything free of light no medium is needed.