You may have two problems:
* you're using coarse vermiculite. The fine stuff is hard to find,
but try small garden outlets. The fine stuff looks sort of like
the dark wet beach sand you see near oceans.
* you haven't plugged up the drain holes in your pots. Use a
strand of spaghnum, or some non-organic non-rotting wicking
material, to mostly plug the drain holes, otherwise your media
will wash out the little holes every time you water,until the
bottom half of the inside of your pot is hollow.