This DIY Kit will allow you to build a (2 x 2.5m pond) at 3 ft deep. Equating to a total of (4500) litres.
 
Pond kit Smart 4,500 litres -
Pond Dimensions: Length 2m; Width 2.25m; Depth 1m
Filter Kit: BioSmart Set 18,000
Liner: Greenseal 1mm thick 4.5m x 5m
Underlay: 250 gsm (white)
Total Litres: 4,500 (Approx)
Max Stocking density: 4 x Koi or Larger species