I'd personally recommend a UV filter and more aquatic plants in the pond- the UV filter will make the algae clump together so it can be caught in the filters sponges, while more aquatic plants will help use up the nutrients and block out the light that the algae thrives off. Algae killing chemicals are not a complete solution (although they do kill off algae), since all the dead algae collects at the bottom of the pond where it turns into a mucky nutrient rich mud, which only fuels future algae blooms.
Most new ponds suffer algae problems in their first year or two, and most of the time these stop- my pond got green water in the summer it was first set up in, but once i the aquatic plants i bought started to establish themselves, i never got anymore algae blooms in the pond again
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A lot of people don't like duck weed, but its actually very effective at preventing algae blooms in ponds since it blocks out the light and uses up lots of nutrients (it also attracts lots of wildlife like dragonflies and mayflies and can help shelter very small fry etc)- its not the easiest of stuff to completely get rid of though, however its very easy to control since you can fish out mats of the stuff with a stick and it doesn't really grow in the winter and IMHO it can look very attractive in small quantities- it is one of natures solutions to getting rid of and preventing green water, which is why i allow it to be in my pond (the weed itself also composts very quickly and makes decent compost), but thats just my take on the stuff
. When i last removed a large section of duckweed from my pond a month or so ago, the water in the pond was wonderfully crystal clear underneath the weed (even in the deepest part, just over 4ft deep, you could see right down to the bottom, it was like crystal clear tap water). About duck weed
http
/blog.shirlsgardenwatch.co.uk/2007/09/gone-fishin.html .
Now the pond is clearing well!
