So, barley straw products didn't become illegal in September 2013. As with most tabloid baloney and scaremongering, usually started in the tabloid rags, about the EU it was nothing more than nonsense.
I use watercress. It's worked in every pond I've had - big and small. Easy to pull out if it gets going too much.
Sue D I think that water hawthorn is a great alternative to lilies. They can withstand a bit more water movement and flower twice a year.
The Water hawthorn is only half hardy though. It's quite expensive if it dies in the winter.
My water cress has attached itself to every root in the pond and is flowering.
With pond maturity comes clarity. My own pond looked like pea soup about a week after being first filled last August. This comes as a result of algae/blanket weed being the first colonisers of a new pond with nutrient-rich water. Introduce higher plants including species that shade the water's surface and they starve the algae/blanket weed of light and nutrients. Result - crystal clear water