Is my UV filter killing my pond plants?

I have a pressurised UV filter controlling the water quality of my garden pond. Is it possible for the UV light to be killing off oxygenating plants such as Mares-tail and Milfoil, as I never seem to have any success with these plants in my pond? Any advice would be welcome.

JEREMY SAYS: UV light being emitted inside a clarifier cannot harm your aquatic plants — a UV clarifier is only damaging to small organisms that pass it while flowing through the filter. This may be bacteria, viruses, disease pathogens or green water, but it won’t harm plants in the pond.

Mares-tail, Hippuris vulgaris, is a native marginal plant, and it may be that you’ve planted it too deep. Place it in a pond planting basket of at least 2 l, with hessian, aquatic compost and gravel on top, then place the basket in 4–10cm of water at the edge of the pond, and it should do fine. True Milfoil is a deeper water plant, so pot it up in the same way but place it 30cm deep in the water.

Spiked water-milfoil, Myriophyllum spicatum, is a British native, but other members of the family, like the closely related Parrot's feather, Myriophyllum aquaticum, are highly invasive and banned from sale in the UK.

Mare’s tail.