Use the largest of the three plumbing options. Larger pipe = less restriction so you will achieve better flow with larger plumbing.
In regards to other advice on the pond filtration, you may want to check out Koiphen.com. There are more people with first hand experience with ponds on that site.
In regards to other advice on the pond filtration, you may want to check out Koiphen.com. There are more people with first hand experience with ponds on that site.
