Ok you've got options. Barley straw will work but if it's pea green your going to need to do something else.
I'm posting blind here as I know not what filters, sunlight is involved.
1: Drastic I know but cover the whole thing, it'll kill off any algae in there but it'll still needs filtering out.
2. Add a UV will keep on top of the problem and do the same as one but still needs, filtering out.
3. Get hold of some heavy duty filter media, really fine and thick stuff, set up a pump to run over this media and it will clear out the algae, I've had to do this years ago a couple of time on my dad's pond, this will need cleaning daily until the water clears.
Good luck, pm me if you need more help