Thanks for that info :). The free swimming tads (great to watch) have already started going amongst the duckweed and starwort(?) < Not sure what it is: small 'star' shaped leaf heads on long stems along the water surface.
It's in this pic, to the left:
The newts hole up during the day under and round the back of that submerged basket! The water has gone clear again since that pic. Now I'm thinking it may have them newt critters stirring it up!
Off to Waitrose now for watercress - They have a small store in town. Otherwise my friend Nina might have some in her fruit 'n veg shop. Her dad has ponds.