No Filter Planted Tank

I'm trying a no filter tank in the office and wonder if there is a
specific FAQ or book recommended for general information.  Specifically,
how does water circulation work in these tanks?  If the plants use up
the available nutrients in the water that is touching them, how does the
water move to provide a continuous supply?  Is Brownian motion enough?

Specifics are 3gal hex, open top, acrylic tank using fine gravel with
peat/soil/clay mix taken from previous tank.  Fertilizer tablets were
added at the recommended rate (Tetra Crypto Dunger) and was planted with
4 pygmy chain swords, 3 anubias nana, a  very small red rubin sword, 2
aquatic shamrocks  and 4 stems of moneywart (??) (I forget the correct
names of these last two).  Lighting is a 15watt florescent suspended
about 6" above the tank.   Inhabitants include a 1" apple snail,
multiple Malaysian Trumpet snails, and I plan to add a betta or paradise
fish.  There will be weekly water changes but no filter, heater or air
stone.  Office temps are in the 70s, light is on a timer.

Rochelle Williams
williaro at ftmcphsn-emh1_army.mil