Forgot to say - got back from work today after being away for a few
days and hence not been messing with the pond. The water is crystal
clear all the way to the bottom. I can see all the fish which has put
me at ease, the Orfe are darting around like mad and the tench are
slowly moving around the bottom - one even came to the top to eat! I
can now see the shape and layout of the pond so probably wont drain and
clean it.

I switch of the pump while cleaning it and for some reason sediment
started to stir up, is this normal? Why does this happen?