Haven't tried a smaller pump. I was assuming, maybe incorrectly, that a smaller pump would have even more restrictions. I'll give that a shot as well. I know some people use Mag drives - maybe I'll try that. I have a note out to Mazzei to see if they suggest a different venturi when using the 2250.

WRT the 2250. It is a very nice filter with lots of room for media - only downsides are the thumbscrews and lack of disconnects. I'll add quick disconnects so that's no issue and I'm thinking about a tool for the thumbscrews so that shouldn't be an issue either. I'm happy you suggested this filter.

Also, for those interested, I found pump curves at ProCooling.com

Update: I got a response from Mazzei. Basically the response was that the 2250 did not have enough flow/pressure to drive any of their venturis. While I agree that it doesn't meet their specs, I would think that I can get the pump to work with a venturi as I was able to produce mist, albeit at a low flow rate. Also, IUnknown has gotten his venturi to work with an Eheim, after changing to a different venturi model. (I'm querying him for details in another thread over at APC. I'll post anything I learn here as I think this is a good methodology).