Hi Adrian, welcome aboard.
Sounds like you have a very interesting collection of pond fish. I would love to see some pics.

The algae have been growing all winter this year. I think it is because of the unusual weather. I agree with telboy, the best thing is to wrap it round a stick, making sure you do not take out any fish or frogs trapped in it. Also use the 'natural' treatment in spring and summer. Better not to use chemical herbicides with the sturgeon and chub.