How broad is the coping at the top of the wall? Perhaps you could suspend planters using brackets hooked onto the wall (think radiator or caravan clothes airers). I haven't done this - coping is too wide for it to be practical - and I have Erics suggestion
The growing medium (grit)would be in the water but the fish couldn't disturb it and the plants will derive nutrients from the water lowering the nitrate levels just like a veggie filter.
Make sure you don't use any material that will be harmful!
Jim
Posted on Nov 2, 2007, 12:05 PM from IP address 81.153.236.138