Hi Mrs Caz and welcome to WAB
We had a similar problem with green algae and blanket weed on a lake. The resident swans were all but forced off one summer because it had grown so thick. Raking it off and into a boat was a mucky job and it didn't solve the problem. The advice we were given was to get bales of barley straw and weight them so they didn't float off, obviously not suitable for a small pond though.
I did find a site that may help...
http://www.lifeforceonline.co.uk/pond_treatments.html
GOOD LUCK!!
Tragus