Try here
http://www.happykoi.co.za/1.%20all%2...filtration.htm

or here http://www.hendersons.co.uk/filtration/page2.html

or here
http://www.koi.com.my/forum/KOI_Talk...Urgent!_P2381/

Don't think I would use a swimming pool sand filter but if you must try one
I would use it last just before you return the water to the pond.

Brushes work well as a coarse filter after the settlement basin. Then a
veggie filter.