In my experimental tank (1" red clay from an Ontario town called Terra Cotta,
1" composted cow manure plus 1-2" of gravel) the C. wendtii roots are
growing straight UP out of the gravel!?! All around the plants, hair-thin root
grow up into the water, 1-2" high. Can it be?

BTW, this substrate is (so far) amazing. All plants are growing extremely well
including the waterfeeders (hornwort) _without_ an algae explosion. There are
some green thread algae, but not much all. Although I don't have any fish in
this tank, I believe the water is very healthy (the snails are multiplying,
there are lots of hydra in the tank, and other microscopic beasties are float-
ing about.)