Stan The Man writes:

[snip]

I think your best bet would be to install a filtration system -
solids-handling pump + mechanical/biological filter + UV clarifier
...or plant some shrubs - sunlight is the main promoter of algae and
you can dramatically improve the quality of your water just by
increasing the amount of shade.

To reduce the sunlight, he's probably better off using floating plants
rather than shrubs. There are quite a lot to choose from at
http://www.bromfieldaquatics.co.uk/ who I've heard good reports about.

Stan

Alan

--
Alan Williams, Room IT301, Department of Computer Science,
University of Manchester, Oxford Road, Manchester, M13 9PL, U.K.
Tel: +44 161 275 6270 Fax: +44 161 275 6280