thanks for your comments, i put split bamboo (which comes on a roll) over the top, it does not block out the sun completely but most of it, i had problems with blanketweed as my pond is in full sun from around 11am, it stopped that problem almost immediately, and to my surprise seems to give my fish a better colour appearance, i've got two filter systems, on one is a titan pump then it goes through a saturn booster pre-filter which then goes through a vorton 14000 uv, then into a trinamic12500, which empties into a small veggie filter i made out of an old box filter then it goes into the pond, on the other filters, i've used a titan pump it also goes through a vorton 14000 then splits and goes through two eco-max filters with built in uv's these also go into the veggie filter then into the pond, all my pond equipment is hozelock, the water is gin clear, as with most of us who care for our fishy friends i check everything constantly and pretty much know every scale on my fish.
mick