flat slate is my favorite aquarium rock.
i like to stand it up so it provides contrast
behind plants, and hiding for fish without
taking space and light away from the plants.
you can lay 2 or 3 flat slate pieces flat
to make a great ledged hiding place.
some algae will grow on slate, but don't
bleach it, just rub it off with a dish pad.
here it comes in light Grey, blue Grey
purple and a marbleized layer color.
be sure to ask the reseller what day
he gets his rocks delivered and try
to show up then for the best picks.