Originally Posted by Kay

You'll use more space by having a substrate - you'll take away depth.
You should use the special aquatic pots which are like plastic baskets.
they don't need to be large - you may be able to get away with 2 inches
square. Aquatic compost - low nutrient, too.

Some of the water weeds don't need soil as such - they just throw roots
into the water. Then you'll also want something to cover some of the
surface - you could use a floating plant.

If you want wildlife, then you'll be best sticking to UK natives. A lot
of plants will be too big or too vigorous. Watercress grows if you just
chuck a bundle in, but grows too quickly - you'll be forever weeding out
the surplus. Water forget-me-not is a good bet and again just throw in a
rooted cutting, also Mimulus (monkey musk). You won't need a lot of
plants.
--
Kay
"Do not insult the crocodile until you have crossed the river"