Damn that about Tropica plant base,I've just ordered a bag!!I've currently got a tank running 100% sand that everything except swords and crypts does well in,I target the roots of these with api root tabs in this tank (Argos playsand).
In my 125,I have a layer of laterite (never clouds when disturbed,I believe this was also API),over which I have eco complete,with a black sand foreground (which is ever so slowly mixing with the eco complete).
I'm about to set up another tank,with the Tropica plant base,pea gravel background and playsand foreground.After my previous experience I'll use a physical barrier to seperate the rear and foregrounds.
On the basis of what was said earlier (I wish I'd known),if you want a nutritious bed that won't cloud to go under your sand,I'd go with laterite.