i would go with alot larger than that...minimal 3000gph for 5000 gals... and that depends on how you plan on stocking this pond,heavy or light? build a good bio filter..there are plans in the diy forum and th equipment forum, look for "my 70 gallon skippy filter" in the diy or 55gallon biofilter in the equipment forum.. these are both the same basic upflow design and both work exceptionally well. you can use a large sturdy outdoor plastic trash can in place of the tub or barrel if you like.. the BRUTE 44 GALLON is a good replacement,available at Lowes and Home Depot.