Chris Oinonen Ehren wrote:


I worry a bit about the duckweed. In ponds it usually signals a not very
healthy pond ecology. It cuts off light to plants beneath it, I tend to
think it cuts down on the surface area of the water, limiting the exchange
between water and air. Of course the hope is that the plants will free
sufficient O2 to take care of the animals' needs, and the light will come
from the side, not down through the duckweed. Still, if it were me, I'd
skip the duckweed.


Note that in a closed system plants can grow only as far as available
carbon (and other nutrients) allows. This is completly different from
the standard aquarium tank, where food and CO2 from the air would indeed
allow mass propagation.

The question really is which plants and animals can live together in
that little biotope, and it might help to have several species to begin
with. Some will wither, others will grow.

Appart from duck weed, there are some other surface-swimming plants with
nice "roots", like _Riccia fluitans_.