Hi all,
Strangely enough a U.V. light is absolutely brilliant for encouraging "filamentous algae", they remove the floating phytoplankton ("green water") and leave the nutrients in place, it is blanket weed heaven.
If you have alkaline water in your pond you will have "Blanket Weed" type algae, what ever you do. It is an entirely natural phenomenon and not damaging to the pond fauna, and it is only if you have a complete coverage that it is likely to be fuelled by excess nutrients and may cause problems when it decays, as light levels fall in the autumn.
The best option is very careful removal of the early flush in the spring and then to ignore it, as it is a key nursery area for many invertebrates (and newt tadpoles etc), and continual removal is actively damaging to the ecology of the pond.
If your pond is shallow (which you want) this will exacerbate the "problem" as the water will warm quickly and the light will reach the layer of filamentous algae on the bottom, triggering photosynthesis, producing O2 bubbles which are retained in the matrix of filaments, and causing the whole mass to float to the surface. If you can shade the surface, and have lots of emergent plants with access to atmospheric CO2, the "problem" will be very much reduced.
Even though it sounds a bit strange a wildlife pond should have relatively little open water, and areas that dry out etc, it is the structures in shallow water that supports the vast majority of the biodiversity.
Have a look here: <
http://www.pondconservation.org.uk/>.
cheers Darrel