I went to a website recommended by members here (Stapeley Water gardens) and
they mention that in a new pond, green water will prevent new plants from
gaining a foothold and establishing themselves due to the lack of light
(makes sense).

They suggested instead of putting fish in, to put loads of Daphnia instead
(for the first season) because Daphnia will eat the Algae that causes the
Green water in the first place and so the Green water cannot form and the
plants will be free to settle in.

Another site told me that Daphnia is a form of water flea that fish like to
eat -My question is then can I fill my pond with Daphnia and put just a
couple of fish in on the assumption that the Daphnia will keep breeding fast
enough to always make sure that there is more than the fish can eat -after
all natural selection dictates that the strong will survive to breed the
next generation and then in theory I'll never ever get Green water.

Will that work or will it just stress the fish that all these fleas are
constantly zipping and darting around the pond?