I need to upgrade my submersible pump and I am looking for something between 3000 to 4000 gph. My pond is 1600 gallons, but I want double the circulation of the water per hr. I need a pump that will last awhile.

My largest pump is a 2600 gph OASE Nautilus. My pump is 10 years old and still works fine. I don't think they make a larger size of that kind. Since I've not had a larger pump, I don't have a brand preference. Normally if you want more than 3000 gph, you get an in-line pump that is out of the water and not a submerged pump. There aren't too many submerged pumps over 3000 gph. Mag-Drive does have a 3600 gph one. See http://thatpetplace.com/pet/prod/206355/product.web

I have the aquascapes 4500 (4500gph) submersible pump, and am pretty happy with it, maybe I should say happy with aquascapes. The first one started making noise at about one year mark, but aquascapes was good enough to replace it at no charge. So far so good with this one.