Dan - I just figured i wanted some good flow. This one pumps 950gph. Thats a lot of flow for just a 29, but it gets cut down by the scwd, the height it has to push the water and is also restricted by the size of the tubing. So i'd say its around 450-500gph now. What size you need depends on what you want to keep. I'd like mostly SPS with some LPS and zoos so more flow is needed. I like more flow in general, keeps the tank nice and clean.