DIY external filter
 

I plan to buy a new pump next year for my 2000 gallon pond. It has goldfish
in and one koi. I would like an external filter but as the pump will cost a
fortune and the pond only exists because I rescued the fish last year from
someone who was about to dump them in a river I don't want to spend more
than I can afford. The pond cost me enough in labour and liner and plants
etc. So, has anyone ever built their own filter or does anyone know where I
might find a 'how to'?